Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/23/16


Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
816 PM CDT THU SEP 22 2016 .UPDATE... Issued at 814 PM CDT THU SEP 22 2016 Forecast appears on track. Patchy fog/drizzle should continue overnight with low cigs in place or developing. WAA kicks in late with HRRR still indicating increasing coverage of rain/thundershowers late. Temperatures look fine for now. && .SHORT TERM...(This Evening through Saturday Night) Issued at 328 PM CDT THU SEP 22 2016 The models have been consistent and agree well through the short term. The large upper level low pressure trough over the southwest U.S. will slowly lift northeast and into Southern Canada/Northern ND through Saturday night. In response to this, a warm front will lift northward across our cwa tonight and Friday. The areas of drizzle and fog along with thick stratus clouds will likely continue into the night with the low and mid level waa. Radar was showing many weak returns this afternoon. The webcams and obs were also showing some drizzle/light showers. Also, have in chances of showers and thunderstorms for tonight and Friday with the waa. As the surface low pressure area moves into SD Friday evening and then onto the north into Saturday, a dry line/cool front in behind will sweep east across our cwa Saturday and Saturday evening. Showers and storms may develop along this boundary as it moves quickly east. Saturday night looks to be dry and breezy with wrap around clouds beginning to advect into the region from the northwest. After a cool day today, it will be much warmer on Friday as the low clouds break up/move north and we mix out the warmer ll air along with some sunshine. Locations in our sw cwa may see the mid 80s. Saturday should become mostly sunny in the dry slot of the upper low with highs mostly in the 70s. .LONG TERM...(Sunday through Thursday) Issued at 328 PM CDT THU SEP 22 2016 Period starts off with an upper level low over the region. Area will be on the cold air advection side of the low Sunday into Monday, with cool temperatures, breezy winds, and potential for showers. Although, there are still some differences noted amongst the models regarding the exact track of the upper low, which does influence shower potential across the area. For right now, will keep low chances in the forecast but did increase chances a bit Sunday afternoon. Removed POPs across the eastern CWA towards the end of the period, which seemed to be hanging onto precip chances too long as the upper low departed. The GFS keeps the low around much longer than the EC, so SuperBlend is picking up on this solution a bit. If the GFS starts to trend more towards the EC, then POPs can likely be removed for Monday night and perhaps even Monday. Looking towards the middle of next week, there will be some cool overnight lows as a surface ridge sets up over the area. Overall, the air mass itself is not terribly chilly, with 850MB temps in the +5C to +10C range. But, given the longer nights, any length of time under clear skies and light winds will allow temps to tumble. For right now, left inherited Superblend temps, but will monitor for potential lowering in the coming days. && .AVIATION...(For the 00Z TAFS through 00Z Friday Evening) Issued at 615 PM CDT THU SEP 22 2016 A mix of mvfr/ifr cigs will continue across the region through tonight and into Friday morning. Meanwhile, a mix of vfr/mvfr vsbys are expected due to fog and patchy drizzle. Late tonight there is a better chance of showers and isolated thunderstorms as a frontal boundary begins lifting north across the state. && .ABR Watches/Warnings/Advisories... SD...NONE. MN...NONE. && $$ UPDATE...TDK SHORT TERM...Mohr LONG TERM...TMT AVIATION...TDK
Area Forecast Discussion
National Weather Service Wakefield VA
1051 PM EDT THU SEP 22 2016 .SYNOPSIS... Low pressure along with a weak frontal boundary will remain stalled along or just off the Southeast and Mid Atlantic coast through Friday morning. High pressure builds over the local area later Friday into Saturday morning. A backdoor cold front drops across the region during Saturday. The center of high pressure slides into southeast Canada during Sunday. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Update... Showers are diminishing across south central VA this evening as another area of precip tries to rotate into interior NE NC. This particular swath of light to moderate rain showers will continue rotating into this area and is expected to remain scattered throughout the evening and overnight hours. Isolated/embedded thunder is possible in interior NE NC, however this minor threat will come to an end later this evening. Otherwise, increased sky cover the rest of tonight while temps/dewpoints are on track with ongoing forecast. Previous discussion (429 PM)... Late this aftn, areas of showers continued to affect cntrl, SE, and scntrl VA, and NE NC, with a few showers still producing heavy downpours. Otherwise, there was a little more brightening of the sky ovr the CWA, with even some sunshine ovr extrm Nrn/NW counties and ovr NE NC counties. As a result, temps climbed into the mid 70s to lower 80s most areas. Lingering low pressure and a frontal boundary along or just off the SE and Mid Atlc coast, will maintain the chc for at least sctd showers ovr the srn/se half of the region this evening into Fri morning. Heavier downpours will diminish during this evening. Lows will range fm the lower 60s to the lower 70s. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/... The combination of nrn stream energy and the coastal low/associated upr trough weakening, will finally result in decreasing pops and rain chcs ending ovr the sse Fri into Fri night. Will carry slight chc to low end chc pops (20-30%) acrs srn/se areas only during Fri. Surface high pressure will build over the region Fri night into Sat morning resulting in dry wx everywhere. Highs on Fri will range fm the upr 70s to mid 80s. Lows Fri night in the mid 60s to near 70. A backdoor cold front will drop acrs the region during Sat, and the cntr of sfc hi pressure will bld twd SE Canada by Sun morning. Will maintain dry wx during this period, with generally a partly sunny sky on Sat. Highs will range fm the upr 70s to lower 80s acrs most of the area. Expect more clouds ovr the Piedmont Sat night. Lows will range fm the mid 50s to the mid 60s. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Medium range period begins Sunday with an amplified upper level ridge/trough pattern, the ridge axis being centered across the TN/OH Valley with a deep trough over Atlantic Canada. This much the GFS/ECMWf and ensembles are in good agreement with. By Monday, the models really begin to diverge however, the GFS and GEFS mean being much stronger than the ECMWF with an upstream trough over the upper midwest by Mon/Tue. this would lead to more of a strong blocking pattern that would keep the eastward progression of upper ridge axis much slower, becoming aligned along the east coast by late Tue/Wed. The CMC is even slower to push the upper ridge off to the east than the GFS/GEFS. Bottom line is a lot of model uncertainty beyond Monday. For Sunday/Mon, surface high pressure is progged to become centered over eastern Canada with a piece of the High ridging down into the northern mid-Atlantic states by Monday. Deep moisture will be pushed south of the local area, but expect more clouds than sunshine for Sunday (except over the eastern shore where more sunshine should prevail). Have also lingered 20% POPS for much of the area Sunday, shifting to the SW and far W zones Sun night/Mon. Highs will average in the low-mid 70s with lows in the upper 50s to mid 60s Sun/Mon. Did more a broad-brushed 20% POP by late Tue-Thu as high pressure becomes centered somewhere off the NE/northern mid-Atlantic coast and deeper moisture and a slow moving front gradually approach from the W. Highs will avg 75-80 F Tue-Thu with lows mainly in the 60-65 F range. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/... Low pressure continues to sit off the South Carolina coast, bringing the region unsettled conditions. Abundant low level moisture and onshore flow will promote widespread IFR stratus...especially in the southeast (PHF ORF ECG) with some IFR vsby. This will be slow to improve Friday morning. Precipitation is diminishing but will still be possible southeast portions...especially at ECG. More favorable conditions are expected by midday Friday with VFR conditions and mainly dry weather across the area as the aforementioned low weakens. OUTLOOK...A cold front sags south through the Mid Atlantic States durIng the weekend. High pressure builds from the north but weakens toward midweek. It will be mainly dry through the outlook period and despite an onshore flow...VFR conditions are expected to dominate. && .MARINE... 10 pm update... Due to an increase in the wind over the Bay and adjacent coastal waters...extended the SCA that was set to expire at Midnight to 4 AM EDT. HRRR handling the winds best. Latest obs reflect ENE flow across the waters as Pressure gradient remains compressed between high pressure well north into New England and weakening low pressure lingering along/just off the SE coast. Seas have dropped off to 4 ft or less for NC waters so have cancelled the SCA headline there (remaining in effect for the rest of the coastal waters and mouth of the Bay). Winds of 15kt gradually drop off from late this aftn through tonight as pressure gradient slackens a bit further. Winds turn more northerly and pick up a bit by Fri night as weak low finally nudges offshore. A weak Cold front drops across the waters late Friday Night into Saturday, stalling just south of the waters Sat night and Sunday before sliding south into the Carolinas on Monday. CAA surge behind the front appears minimal...but SCA for hazardous seas possible over the weekend as longer period swell begins to mix in Friday night through Sunday. && .HYDROLOGY... The Cashie River at Windsor crested at 15.0 ft late this morning...with the most current level at 14.5 ft and slowly falling as of 715 PM this evening. This water level is still within major flood stage, which begins at 13 ft. Although light rain showers are expected to continue overnight through Friday afternoon before ending, the Cashie River near Windsor is forecast to steadily fall over the next several days...possibly dropping below flood stage completely by roughly Sunday afternoon. && .TIDES/COASTAL FLOODING... As of 17Z, tidal departures continue to avg +0.5 to 1.0 ft over the marine area, but no tidal flooding is occurring and no advisories are needed at this time. Will continue to monitor however, as tidal anomalies may build nwd through the Bay by later this aftn which could lead to some marginal tidal flooding by this evening farther up into the Bay. Moderate risk for Rips expected for Thu. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...Small Craft Advisory until 10 AM EDT Friday for ANZ650-652-654. Small Craft Advisory until 4 AM EDT Friday for ANZ634-656. && $$ SYNOPSIS...TMG NEAR TERM...BMD/TMG SHORT TERM...JDM/TMG LONG TERM...LKB AVIATION...LSA MARINE...LKB/LSA HYDROLOGY... TIDES/COASTAL FLOODING...
Area Forecast Discussion
National Weather Service La Crosse WI
830 PM CDT Thu Sep 22 2016 .UPDATE... Issued at 830 PM CDT Thu Sep 22 2016 The trends in the hi-res meso scale models have been consistent through the afternoon into this evening of the convection that develops tonight north of the stalled front across Iowa to primarily be confined to northeast Iowa into southwest Wisconsin. Activity has been developing north of this front along Highways 20 and 30 across Iowa, which is close to what the HRRR has been suggesting. While locations in the Interstate 90 corridor may see some rain overnight, not expecting it to be all that heavy so opted to trim back the flash flood watch to just northeast Iowa and southwest Wisconsin. && .SHORT TERM...(Tonight and Friday) Issued at 318 PM CDT Thu Sep 22 2016 Rainfall records continue to be set and rivers continue to rise. We have reached a vulnerable point where forecast rainfall is of utmost importance. Good news is there may be some relief in sight. We continue to watch progression of large upper low moving through western U.S. Unlike past few days, minimal signs of an upstream short wave to focus low level response into boundary that divides very moist airmass to the south and drier, cooler airmass north. Combined with backing flow as upper trough digs in west, seeing signs in short term model data that main moisture transport and focus will be shifting more west for tonight. Nonetheless, primed airmass remains along southern tier with higher precipitable water values and some convergence. Convection has slowly been on the increase closer to Highway 20 area in Iowa, closer to CAPE gradient region. As the evening goes on, would expect this focus to gradually shift north unless convection becomes extensive enough to hold boundary where it is at. Still concerned if convection does spread north, we could see another 1-2" of rain so will keep Flash Flood Watch going at least into Friday to cover any threat. Given how saturated things are, anything over a half inch could pose a problem. On Friday, as upper flow continues to back and becomes more southerly, may see remaining area of elevated convection gradually shift north and east as it dissipates. Banking on coverage being on the lighter side with loss of forcing. Also hoping this leads us into a period of dry weather and flood headlines can be cleaned up a bit. .LONG TERM...(Friday night through Thursday) Issued at 318 PM CDT Thu Sep 22 2016 As previously mentioned upper low lifts northeast over the weekend, could see lingering dry spell Friday night into Saturday ahead of approaching cold front. Models in fair agreement bringing elongated north-south band of rain with cold front passage Saturday night into Sunday. Some model differences on timing with 22.12z NAM the fastest to move rain through, and the GFS/ECMWF more alike holding it back more, but still not as bad as previous model runs had. Convection may not be as intense as earlier this week, but prolonged (?) which could bring more concern for areas hard hit by flooding. Will certainly have to watch how this plays out and future flood watches may be needed. Now for the really good news. Drier flow regime looks in the offing for much of next week, although some differences in medium range guidance. 22.12z ECMWF is far more progressive sweeping upper low by and northwest flow sets up with eventual upper ridge building in. GFS is a bit slower with this evolution and swings upper low into Great Lakes. This might not generate as much rain but may hold back temperatures far more than ECMWF. Blends of operational models suggests a small chance of rain into mid week but we could see a lot of dry time in there. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 604 PM CDT Thu Sep 22 2016 A weak boundary was across southern Minnesota into northeast Wisconsin late this afternoon with the main surface boundary across central Iowa into southeast Wisconsin. The convection so far as been just north of the southern boundary and well south of both airports. A mixed bag of ceilings along and north of the northern boundary with VFR going down to MVFR. Plan to start both TAFs with VFR conditions and then go down to MVFR ceilings by the middle of the evening. Some potential, all be it a small one, that some showers could impact both airports overnight once the low level jet starts to interact with the southern front. Think most of this activity should stay to the south though and have just shown a VCSH overnight. More likely to occur is the ceilings going down to IFR at KRST overnight with some MVFR fog forming at both airports. The winds aloft off the 22.18Z NAM forecast soundings look too strong to allow much of visibility restriction. The forecast soundings do not show much potential for the ceilings to improve Friday so will only show some minor improvements through the day. && .HYDROLOGY... Issued at 318 PM CDT Thu Sep 22 2016 Many areas saw 4 to nearly 12 inches of rain last few days. Combined with recent wet periods most area rivers into flood. Potential for another 1 or 2 inches tonight could generate more problems but confidence in that is low given weaker forcing tonight and boundary further south. Concerns are shifting from immediate flash flood threat to high water or areal concerns, along with river flooding. Also look for continued rises on the mainstem of the Mississippi River going into next week, which could lead to an increase in flood warnings there. Water levels will be fall slower than normal as well given how saturated everything is. && .CLIMATE... Issued at 318 PM CDT Thu Sep 22 2016 La Crosse WI... Top September rainfalls... 1. 10.87 inches in 1881 2. 10.52 inches in 1965 3. 10.33 inches in 2016 4. 10.01 inches in 1884 5. 9.84 inches in 1901 Rochester MN... Top September rainfalls... 1. 10.50 inches in 1986 2. 9.95 inches in 2010 3. 8.96 inches in 2016 4. 8.08 inches in 1978 5. 7.95 inches in 1938 && .ARX WATCHES/WARNINGS/ADVISORIES... WI...Flash Flood Watch through Friday afternoon for WIZ054-055-061. MN...None. IA...Flash Flood Watch through Friday afternoon for IAZ008>011-018- 019-029-030. && $$ UPDATE...04 SHORT TERM...SHEA LONG TERM...SHEA AVIATION...04 HYDROLOGY...SHEA CLIMATE...SHEA
AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
700 PM CDT Thu Sep 22 2016 .SHORT TERM.../This evening through Friday/ Issued at 307 PM CDT Thu Sep 22 2016 The situation is still conducive for heavy rains tonight but hopefully not to the same extent as yesterday. Water vapor imagery does not show the moisture fetch to the same degree as was shown Wednesday, but there is a decided back edge to the vertical motion passing through the Plains into western KS/NE which should aid lift into the night. This has resulted in weak but broad mid level kinematic forcing with a ribbon of somewhat favorable mid level temp and theta-e lapse rates from KS into IA. Thermodynamically the forcing is somewhat better with 850/700mb warm advection noted into IA and 0-2km moisture pooling into our baroclinic zone as well. 20Z surface analysis shows at least two boundaries, one tied into low pressure near Lincoln between Red Oak and Atlantic, another farther northeast through the Des Moines metro area more associated with previous MCS outflow and likely another from Estherville to Grinnell with seems to be immediately associated with the weak MCS. This will provide for ample isentropic lift into the night, but the flow is weaker along the 305K inflow surface vs last night, down to 15- 30kts. RAP elevated instability layers suggest elevated CAPEs will reach uncapped 1500 j/kg later tonight sustaining additional MCS development. There could be a few strong to severe storms, but overall the Marginal Risk seems fine due to reduced effective shear. .LONG TERM.../Friday night through Thursday/ Issued at 307 PM CDT Thu Sep 22 2016 Expecting some early morning ongoing convection across the eastern and northeastern areas to end by mid to late morning. Warm front will finally retreat north into the afternoon hours with rather warm and humid conditions across the area for the remainder of the day. Some cloud cover extending across the northeast with light showers then will give way to some sun in the afternoon. As has been advertised...highs will warm into the upper 80s to lower 90s over the south with the upper 70s in the far north by late day Friday. No rainfall is expected until the long wave trough approaches Saturday morning with showers and thunderstorms moving into Central Iowa by mid to late afternoon. Remnant tropical moisture from Paine will probably still be available at this time across our area. With a ribbon of higher precipitable water and decent convergence along the boundary...will likely see a decent rain event with up to an inch additional from Saturday evening through Sunday. Once this feature pulls east...the models are in some consensus for next week. Both the Euro and GFS now suggest that the H500 long wave trough will keep the moisture channel south and east of the region. This should allow for a period of little to no precipitation and help the river situation across the area. Temperatures next week look cooler and more seasonal for the first week of fall. && .AVIATION.../For the 00Z TAFS through 00Z Friday evening/ Issued at 700 PM CDT Thu Sep 22 2016 Additional thunderstorms and showers expected to develop by late evening into the overnight hours. Expect main impacts to be at KFOD and possibly KALO, KMCW, and KDSM as the activity spreads across the state overnight. Potential for continued development near the KFOD area into early Friday, thus highlighted for now with a VCSH. As trends become more apparent, will fine tune the mentions. CIGS MVFR to low VFR overnight and may have some IFR across KFOD. && .HYDROLOGY... Issued at 307 PM CDT Thu Sep 22 2016 Magnitude and placement of the heavy rains will be key tonight. As mentioned above the environment is not as favorable as last night but still supports heave rain. The surface based potential is trying to recover with uncapped 1500-2500 j/kg MLCAPEs now in place over SW IA. This recovery may be too late to get anything going, but will likely aid slightly elevated convection just to the north and east tonight. The latest objective analysis pegs 0-2km moisture convergence along the Highway 20 to 30 corridors so this will be the favored location, likely anchored along or just south of the current Waterloo MCS which won`t go away. Precipitable waters are already around 2 with warm cloud depths higher than yesterday to 4km. Thus the moisture transport and instability components will not be as good as yesterday, but efficient rains are still anticipated. This will result in 1 rainfall amounts through the aforementioned favored corridor with locally higher amounts from 2-3 possible, thankfully south of where yesterday`s heavy rain occurred. Storms will not be fast moving with a mean of only 15-20kts and Corfidi vectors slow to the south. Thus have kept the flash flood watch in place through 18z Fri and expanded down to the full Highway 30 corridor from Guthrie County eastward. A small section of west central IA counties has been canceled however, which does not seem to be under the gun and didn`t receive much rain overnight. && .DMX WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch through Friday afternoon for IAZ004>007- 015>017-023>028-034>039-046>050. && $$ SHORT TERM...Small LONG TERM...REV AVIATION...Beerends HYDROLOGY...Small
Area Forecast Discussion
National Weather Service Quad Cities IA IL
901 PM CDT THU SEP 22 2016 .UPDATE... Issued at 859 PM CDT Thu Sep 22 2016 I have issued a flash flood watch for our Highway 20 counties in northeast Iowa, where storms are already beginning to train and move over the same locations repeatedly. With PWAT values around 2 inches overnight, these could easily produce rainfall amounts of 2 to 4 inches, possibly more in locallized areas. The HRRR suggests storms should continue to be active overnight, possibly through mid morning, and that will be how long I carry this watch. && .SYNOPSIS... Issued at 345 PM CDT Thu Sep 22 2016 Remnants of the larger MCS last night in northern IA/southern MN which dropped 4 to 10 inches of rain continues to fester in the form of scattered showers and isolated thunderstorms in the dvn cwa. This is mainly north of Interstate 80 along a CAPE gradient. Extensive cloud cover was keeping instability in check in the north with 3 pm temperatures in the lower to mid 70s. More sunshine in the far south was allowing for temperatures near 90. Looking to the west, skies were sunny in western and central IA where the better low level convergence, stronger deep layer shear, steeper lapse rates and higher CAPES were located. This is where additional convection should fire later this afternoon. Haase && .SHORT TERM...(This Evening through Friday) ISSUED AT 345 PM CDT Thu Sep 22 2016 Forecast focus on thunderstorm chances mainly north. Tonight: CAM`s models indicated thunderstorms to fire across northern/central IA later this afternoon and evening. These storms should then push eastward across roughly the northern half of the dvn cwa this evening and overnight. The ECMWF/GFS is a bit farther south with the heaviest rain axis compared to the HRRR. The better coverage of storms should be in eastern IA and northern IL along and north of Interstate 80 so this is where the highest pops will be. Some of the storms may produce locally heavy rainfall of potentially at least an inch or two. Any repeating storms over the same area may produce several inches of rainfall in a short time with PWAT`s approaching 2 inches. There is still uncertainty of where exactly the highest rain amounts will fall tonight with variance in the models. Later shifts can monitor convective trends and adjust pops if needed. Minimum temperatures should be in the mid to upper 60s. Friday: Scattered thunderstorms are possible over most of the cwa in the morning then the storms should shift northward as an upper level ridge/building heights shifts into the area. This will push the warm front northward into Wisconsin as the day progresses. Much of the afternoon should be dry except we will still carry a chance pop in the north. Highs should be in the upper 70s along Highway 20 to the mid to upper 80s elsewhere. This will again be a warm and humid day at most locations with dewpoints well into the 60s. Haase .LONG TERM...(Friday Night through Thursday) ISSUED AT 345 PM CDT Thu Sep 22 2016 Friday night and Saturday, an upper ridge will traverse the forecast area with mainly dry and unseasonably warm conditions. Saturday night and Sunday, active weather will return with sharp southwesterly flow aloft and a slow moving cold front oriented parallel to the upper flow. Precipitable water values are expected to rise close to 2 inches once again. This scenario will be favorable for additional heavy rain, especially across eastern Iowa, which will be crucial regarding river flooding next week. The potential for severe storms is minimal due to a number of factors, including timing and relatively weak deep layer shear. RPK Sunday night...Latest trends(more progressive) on the various medium range models suggest a post-frontal shower regime laying out mainly along and east of the MS River Valley, which would ideally be away from the swollen IA tributary rivers. Both the 12z NAM and ECMWF mainly have light rainfall amounts of 0.15 inches or less in these areas, while the 12z GFS is more bullish with post-frontal moisture stream making for 0.25 to over a half inch of additional rainfall from the MS RVR on eastward. For now will take a QPF blend and migrate POPs more toward the east. Monday and Tuesday...Large model descrepancies start popping up with the major medium range players the 12z GFS and ECMWF early next week. The GFS blocks a nearly stacked cyclone acrs far northern MN, while the new ECMWF is further north and more progressive with the upper trof migrating the main axis toward James Bay by Monday evening. Both models are basically dry for Monday for different reasons, the GFS with the CWA under in-whirling dry slot into the MN cyclone center, while the Euro starts exiting out broad cyclonic flow in favor of upstream ridging. Highs mainly in the 60s on Mon. Model differences really apparent on Tue with The GFS wrapping around instability showers acrs the northern half of the CWA Tue afternoon, while the 12z ECMWF maintains dry, in-building ridge regime and near normal temps in the upper 60s to lower 70s. For now will have to maintain low/slight CHC POPs with the descrepancies but at least that is a drier trend. With a cloud clear out, Tue night lows will be down in the 40s for most of the area. Wednesday and Thursday...Longer range trends are for an Omega Block type pattern to set up shop acrs the mid CONUS somewhere, which would translate to welcome mainly dry weather and seasonable temps for the mid to late week period. But again, the latest run medium range models especially the GFS/ECMWF, vary in placement of their mean axis. The GFS keeps a trapped/blocked cut-off upper low far enough to the west acrs the western GRT LKS to spiral more showers back acrs the area Tue night into Wed, while the Euro progresses the Omega Block axis eastward to the MS RVR Valley basin by late Wed night and continues a basically dry regime into day 7 of the forecast. Again with the descrepancies, will keep low POPs for showers mainly acrs the northeastern to eastern half of the CWA Tue night and Wed, then dry for Thu. But if additional model runs continue to progress with the incoming pattern regime, see the drier ECMWF solutions winning out for mid next week. Temps may generally be in the 60s to around 70 for highs, and lows in the 40s. Clouds will make for cooler highs and milder lows in spots if cyclone wrap around stratocu maintains more or hangs on with higher coverage than currently expected. ..12.. && .AVIATION...(For the 00Z TAFS through 00Z Friday Evening) ISSUED AT 623 PM CDT Thu Sep 22 2016 Showers and thunderstorms will be possible this evening and overnight, in all areas of eastern Iowa and northwest Illinois. This will result in a forecast of vicinity showers in all locations for this evening, but with a more organized round of storms expected tonight in northern Iowa, I have put in a tempo group for thunderstorms at DBQ. Some periods of MVFR are possible in light fog toward sunrise, but otherwise mainly VFR weather is expected outside of thunderstorms. Winds will be light and variable except near storms overnight, and should become steady south to southeast again during the day Friday. ERVIN && .HYDROLOGY... Issued at 345 PM CDT Thu Sep 22 2016 Overview: Repeated rounds of very heavy rain have occurred over northern Iowa, southeastern Minnesota, and western Wisconsin over the past three days. A widespread 3 to 5 inches of rain has fallen with isolated amounts of 6 to 9 inches. Additional heavy rainfall is possible tonight and again Saturday night in the same general area. These extreme rainfall amounts will result in significant river level rises downstream into eastern Iowa, including the Mississippi River, into next week. The majority of local river sites are now under either a flood warning or flood watch as significant rises are forecast to begin this weekend or early next week. Warnings: On the Cedar River, Iowa River, Wapsipinicon River (De Witt 4S), and Mississippi River (sites Dubuque LD11 and Dubuque) Confidence...Moderate on river level forecasts. Uncertainty arises with respect to forecast crests, not on whether river levels will exceed flood stage. How high rivers rise above moderate or major flood stage is dependent on the downstream propagation of upstream runoff. As new data is gathered over the coming days, forecast confidence will likely increase. Watches: on the Mississippi River (all sites except Dubuque LD11 and Dubuque) and Wapsipinicon River (Independence and Anamosa). Confidence...Low to Moderate on river level forecasts because river levels will depend on the amount of runoff that is routed downstream through several tributary rivers. As new data is gathered over the coming days, forecast confidence will likely increase. && .DVN Watches/Warnings/Advisories... IA...Flash Flood Watch through Friday morning for Buchanan-Delaware- Dubuque. IL...NONE. MO...NONE. && $$ UPDATE...Ervin SYNOPSIS...Haase SHORT TERM...Haase LONG TERM...12/RP Kinney AVIATION...Ervin HYDROLOGY...Brooks/Uttech
Area Forecast Discussion
National Weather Service Hastings NE
700 PM CDT THU SEP 22 2016 .UPDATE... Issued at 649 PM CDT Thu Sep 22 2016 Updated the forecast tonight to expand the area of fog mentioned tonight to include some areas along and just south of I-80 from near Kearney and farther west where stratus stuck around longer today. Am contemplating hitting the fog a bit harder than we have in the forecast, judging by later HRRR runs. && .SHORT TERM...(This evening through Sunday daytime) Issued at 417 PM CDT Thu Sep 22 2016 Forecast highlights/overview of these next 72 hours: The primary concern through these 72 hours centers around the still-somewhat- unclear rain/thunderstorm chances centered on the Friday night- Saturday night time frame (rain chances/PoPs have been held below "likely" 60+ percentages at this time due to inherent uncertainty in coverage). Assuming that at least isolated/scattered activity is able to develop during this time frame, a few strong to severe storms are not out of the question, especially Saturday afternoon within eastern parts of the CWA. Turning back to the nearer-term, have left the forecast void of any mentionable (meaning 15+ percent) shower/storm chances through tonight, but these chances are not necessarily "zero" either. There is some concern for at least patchy fog development mainly within counties along/especially north of I-80 tonight, with a few higher-res models such as the HRRR suggesting that this fog could be a bit more widespread/impactful. For now, have not gotten very aggressive but did at least introduce a mention of "patchy fog with visibility less than 1 mile" to tonight`s forecast. Temperature-wise, unlike today, Friday is expected to have a more uniform temperature regime with well-above normal heat in all areas. Then, a gradual cool-down should occur over the weekend, with highs by Sunday actually slightly below normal (and roughly 20 degrees cooler than Friday). Taking a look at the current scene as of 330 PM (and as outlined in the "update" discussion earlier this morning)...sky cover/temperature forecasting has been a bit of an "adventure" today thanks to a stark division between widespread sun/heat over southern/eastern counties and a nearly solid deck of low stratus clouds over many northern/western counties. As expected, the southern/eastern edges of this low stratus has in fact slowly retreated/eroded off to the north and west in response to daytime heating and mixing. Gave a "best shot" at where actual high temps will end up, but currently it appears a rather big gradient from low-mid 70s far north/west-central...mid 70s to low 80s in the central Tri-Cities area...and noticeably hotter upper 80s to low and even mid-90s in far eastern and southern counties (hottest of all in our southern-most KS zones). At the surface, the edge of this stratus is fairly closely tied to the position of a nearly- stationary front that is draped across the CWA from west-southeast to east-northeast. Fairly light north/northeast breezes prevail north of this boundary while southerly breezes prevail to its south...and a hodge-podge of light/variable in between. In the mid-upper levels, a period of weak/subtle ridging appears to be in control of the Central Plains between a departing shortwave over IA, and a powerful/highly-amplified trough over the western CONUS featuring a deep closed low centered over NV. Now looking ahead forecast-wise through these next 6 day/night forecast periods... This evening/tonight: Despite various hints in various models that at least spotty shower/thunderstorm activity could at least flirt with the fringes of our CWA (especially northern areas after dark), decided that the overall coverage of any of this possible activity within our borders would remain closer to 10 percent than 20 percent, and thus these chances are below mentionable thresholds (in other words, the forecast reads as "dry" but please note that chances are not necessarily zero). Certaintly, the most legitimate rain/storm chances tonight should focus north of our CWA from northern NE eastward into IA, where mid level temps are a touch cooler and where there is better convergence near the nose of a modest low level jet. At the surface, the aforementioned front draped across the heart of the CWA will slowly lift northward as a warm front overnight in response to low pressure deepening to the west, turning breezes more southerly as it does so. It is still unclear exactly what the low stratus deck does, as its northward-retreat is likely to stall out for a time around nightfall, keeping it stubbornly over our northern/west-central zones well into the night before eventually vacating our CWA for good. As mentioned in the opening paragraph, there are hints of fog development overnight mainly in counties north of the I-80 corridor, and have introduced a generic "patchy with visibility less than one mile" to get the ball rolling this direction. Temp- wise, if anything nudged down lows very slightly, aiming for mid- upper 60s most areas but low 60s far north. Friday daytime/night: This is "part 1" of our upcoming rain/storm chances, and confidence is pretty high that they will not even arrive in western zones until after dark. In the mid-upper levels, the aforementioned deep western trough will gradually approach/invade the Central Plains, with its primary mid level vort max reaching western WY by late afternoon, and into southeast MT by daybreak Saturday. Ahead of this system, confidence remains rather high in a dry, mostly sunny and very warm (some would say hot) day with noticeably breezy southerly winds overtaking the entire CWA as the warm front blasts well to our north. Made little change to high temps/winds, as the entire CWA is expected to top out 88-91 in the presence of sustained south winds 15-25 MPH and gusts 25-25 MPH, highest in the afternoon. Then, as the night wears on, forcing gradually increases from the west, and fairly low chances for isolated to perhaps scattered of showers/thunderstorms arrive to the western CWA before midnight and then expand CWA-wide late in the night. Can`t completely rule out a rogue strong to marginally severe storm mainly with hail, but this should be the exception. The invading north-south oriented synoptic cold front may be right on our western doorstep by night`s end, but ahead of this boundary low temps should hold up mid-upper 60s most areas. Saturday daytime/night: This is "part 2" of the storm chances, but confidence in areal coverage of this rainfall is still not high enough to justify "likely" PoPs within the CWA. Certainly though, chances are higher in southern/eastern counties than they are in northern/western counties (which could really end up missing out on things). In the mid-upper levels, the main vort max swings north toward ND during this time, while the large-scale trough trailing to its south slowly edges east through the Plains. Meanwhile at the surface, barring some fairly big changes, models have seemingly settled on a steady west-to-east progression of the synoptic cold front through the CWA during this time. Based on instability/shear progs and the timing of the boundary, especially our eastern-most counties may see at least a brief severe storm threat Saturday afternoon along this front, and agree with the SPC putting these areas in a Marginal Risk. This will bear watching, because if the front slows at all, then more of our CWA may be in a severe risk mainly for large hail/wind. Taking the latest models literally (especially the NAM) suggest that the majority of shower/storm chances may be over with by sunset. However, models such as the ECMWF/GFS are slower with precip departure, and thus will linger modest PoPS through the night especially in eastern/southern zones. High temps are aimed low 80s most areas and with With cooler air invading, lows expected to drop into the 50s nearly all areas. Sunday daytime: Although it could be a close call in extreme southeast zones, confidence was high enough to leave the entire CWA void of shower/storm chances behind the departing cold front. As a result, we are looking at a "fallish" day featuring plenty of sunshine, cooler temps and breezy northwest winds averaging 15-20 MPH with higher gusts. If anything, nudged up highs 1-2 degrees given expectation of sun/decent mixing, aiming for 69-72 most areas. .LONG TERM...(Sunday night through Thursday) Issued at 417 PM CDT Thu Sep 22 2016 Fall-like conditions are forecast to continue on into the beginning of the next work week, with temps climbing back to normal by mid- week. The main change made to the forecast for the long term was to remove precipitation chances. At the start of the period, models are in pretty good agreement showing the main upper level trough axis continuing to push through/east of the CWA. By 12z Monday, the axis looks to extend from central MN south through central KS, with northwesterly winds in place across the CWA. That northwesterly flow aloft remains in place through at least Mon/Tues, as ridging over off the west coast starts pushing east through the Rockies. As we get into Wed/Thurs, that ridging moves onto the Plains/right over the CWA. The 12Z run of the ECMWF/GFS are in good agreement showing little in the way of disturbances moving through, keeping this dry. The 12Z run of the Canadian is an outlier, keeping a massive cut off lower pressure system over the central CONUS through the period. At the surface, high pressure builds into the region behind the weekend frontal passage, with light, northerly winds on Monday turning more variable for Tuesday. Return southerly flow looks to return for mid-week. As far as temperatures go, not expecting a lot of change for Mon/Tues compared to Sun, with highs generally in the mid-upper 60s and dewpoints in the 30s and 40s. Warmer temps forecast for mid-week with the upper ridge building in, reaching the mid 70s by Thursday. && .AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Friday evening) Issued at 649 PM CDT Thu Sep 22 2016 Biggest issue will be low-level wind shear overnight as a low- level jet develops. We will be on the northern edge of concern. Also, visibility may lower as we were on the southern edge of where stratus stuck around for much of the day, so confidence is really not high here. && .GID Watches/Warnings/Advisories... NE...None. KS...None. && $$ UPDATE...Heinlein SHORT TERM...Pfannkuch LONG TERM...ADP AVIATION...Heinlein
Area Forecast Discussion
National Weather Service Green Bay WI
1001 PM CDT THU SEP 22 2016 Updated aviation portion for 06Z TAF issuance .SYNOPSIS... Issued at 223 PM CDT Thu Sep 22 2016 A break in the excessively wet weather, but temperatures remaining near or above seasonal normals. Currently on the large scale, strong Pacific jet splits near the West Coast before merging back together in the Great Lakes region. The pattern will be slowly progressive, especially early in the forecast period. Ridging building northeast from the eastern Pacific will force the location of the split eastward into the Plains by the weekend. Thereafter, the evolution of the flow regime becomes uncertain as the medium range models offer varying ideas on the handling of the remnants of the current southern stream upper trough. That uncertainty will impact precipitation chances during the latter part of the forecast period. Temperatures are expected to remain near to modestly above seasonal normals through most of the the period, though they could tail off late. Shower chances will continue the next couple days, especially across the southern part of the forecast area. But rainfall amounts should remain on the light side. Precipitation chances during the middle to latter part of the period will depend on the evolution of the current southern stream upper trough now over the western CONUS, and thus are a low-confidence aspect of the forecast. The best estimate is that rainfall totals for the next 7 days will end up AOA normal, though at this point amounts do not look excessive. && .SHORT TERM...Tonight and Friday Issued at 223 PM CDT Thu Sep 22 2016 The latest RAP analysis and satellite/radar imagery show a nearly stationary surface cold front stretching from west-central WI to near Wausaukee early this afternoon. Scattered morning showers died off along the boundary by midday, but the hi-res models continue to indicate that a few showers will be possible over east-central and far northeast WI and within a pwat axis through the rest of the afternoon. Not convinced that will occur since there is little to no instability, but left a small chance just in case. Observations also indicate the presence of some drizzle over far northwest Wisconsin within a band of low clouds behind the front. Some of this drizzle could move into Vilas county later this afternoon. As the front finally makes a move southward tonight, small precip chances and cloud cover are the main forecast concerns. Tonight...The cold front will finally move south across central and northeast WI this evening, and into southern WI overnight. Position of the pwat axis and hi-res models indicate that east-central WI could see a shower or two early in the evening before the front exits the forecast area. But will leave a slight chance across the south in case the front is slower to exit than progged. Otherwise, should see widespread cloudiness linger behind the front per satellite imagery. A developing northeast breeze should keep the boundary layer churned up to limit fog potential even after all of the rainfall. Lows falling to near 50 in the north to near 60 in the south. Friday...The cold front will settle over far southwest Wisconsin and northern Illinois. A band of low clouds are expected to remain behind the front, which should keep central and east-central WI more cloudy than over northern WI, where northeast winds will push in drier air. Cannot rule out a few showers over central and east- central WI in a region of modest mid-level fgen. Because of more sunshine, northern WI could be as warm or warmer than locations further south. Will go with highs mostly in the mid 60s. .LONG TERM...Friday Night Through Thursday Issued at 223 PM CDT Thu Sep 22 2016 Weak isentropic lift will begin spreading back across the area Friday night. That seems worthy of having chance PoPs expand northeast across most of the area during the night, though with limited instability opted to leave thunder out of the forecast. Though confidence in precipitation forecast for the rest of the period is probably lower than normal, leaned toward the ECMWF for PoPs. The 12Z EC was fairly consistent with its previous run, and exhibited decent consistency with the GFS ensemble mean. That resulted in a prolonged period of chance PoPs as the upper trough crosses the area. The best chance for rain looks to be Sunday and Sunday night, though that could easily chance in later forecasts. No significant changes were necessary to the extended forecast initialization grids based on a broad blend of guidance products. && .AVIATION...for 06Z TAF Issuance Issued at 951 PM CDT Thu Sep 22 2016 Late this evening, a surface front is shifting south of Wisconsin while an 850 front slides southward over the state. A mix of IFR and MVFR cigs with isolated light showers or sprinkles will be associated with this 850 front. Patchy fog will also be possible tonight. Drier air pouring in from the north should improve northern and Northeast Wisconsin to VFR conditions Friday morning as high pressure drifts over the northern Great Lakes Region. Cigs over Central and East Central Wisconsin may improve to lower end vfr cigs later Friday morning, with scattered showers lifting back north as the surface front begins to move north again. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS.......Skowronski SHORT TERM.....MPC LONG TERM......Skowronski AVIATION.......TDH
Area Forecast Discussion
National Weather Service Wilmington NC
1050 PM EDT Thu Sep 22 2016 .SYNOPSIS... Weakening low pressure will drift offshore of the Carolinas through late Friday, taking the rainfall threat with it. Weak high pressure accompanied by drier air will prevail on Saturday. A modest cold front will drop south across the area early Sunday. Modest high pressure will follow and ridge across the area from the NE states through the early to mid week period of next week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... As of 1015 PM Thursday...Still have active pcpn affecting the area, and should continue for much of the overnight. The sfc and upper lows are straddling the coast along Horry and Georgetown counties, and is trying to make some headway along the coast to the NC-SC border by daybreak Fri. The activity will transition to mainly over the adjacent Atlantic Waters and occasionally moving onshore affecting the coastal counties during the pre-dawn hours and into daytime Friday. The activity may further increase in coverage and intensity during daytime Fri due to the availability of insolation and in turn increased instability. Will continue to highlight the HWO with possible flooding and ponding across vulnerable locations, especially areas that have received a plethora of rainfall during the past 12 to 24 hrs. Minor tweaking applied to overnight temps/dewpts due to pcpn occurrence. No changes to the Min temp fcst Previous................................................. As of 600 PM Thursday...POPs have been increased thruout this evening with the going concern being the continued moderate to heavy rain being produced by the convection. Lightning data has been limited/sparse across the Carolinas and therefore will just mention isolated thunder thru mid-evening. With the moderate to heavy rain persisting well into this evening, unlike what the latest HRRR and RAP indicate, have updated the pcpn phraseology to include "heavy rain". In addition, with a half a dozen of Flood Advisories issued, have updated the Hazardous Weather Outlook to include the potential for temporary ponding or shallow flooding from this evenings local heavy rains. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/... As of 300 PM Thursday...Low pressure over the Cape Fear area will weaken and move east through Friday as high pressure builds down from the north. The main mid to upper trough will lift off to the north and east and a ridge builds over the southeast, although both the ECMWF and the GFS show a low cutting off from the main trough and lingering across the deep south into Sun. A weak backdoor front will make its way south through VA and into NC Sat night and should reach into SC by Sun morning. Pcp water values up close to 1.9 inches on Fri mainly aligned along the SC/NC coast will diminish to less than 1.5 inches by Sat aftn with drier air and subsidence finally scouring out the remaining moisture from this persistent remnant low from Julia. Therefore, will continue with higher pops and greatest chc of shwrs/tstms on Fri mainly east of I-95 to the coast as sfc low remains just off the tip of Cape Fear. Expect clearing to occur through late Fri into Sat as Dry air and subsidence work there way south and east as upper ridge builds east through Saturday. This should produce plenty of sunshine across much of the area, but lingering moisture along the coast should produce some cu and possibly some isolated showers mainly over the SC coast Sat aftn. Not expecting much change in the feel of the air mass with humid weather continuing. Clouds will be tough to break on Fri with continued showers and therefore expect high to be in the 70s much of the day, but places that break out in the afternoon should reach into the 80s. Saturday will warm well into the 80s with a good deal of sunshine across much of the area. Overnight lows will be in the mid 60s to around 70. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 300 AM Thursday...A mid-and-upper level ridge axis will shift from the TN valley Sunday to the east coast by Tuesday, and will amplify between two anomalously strong upper lows into a Omega block-type pattern. At the surface, high pressure will ridge down across the mid-Atlantic states and produce onshore flow through the period. Although the primary belts of deepest moisture will remain south and west of the area, persistent onshore flow below 850 mb would provide sufficient moisture to support scattered showers. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/... As of 00Z...Periods of MVFR possible tonight as scattered showers and thunderstorms move across the area. MVFR/IFR anticipated late overnight into early Friday morning due to areas of low cigs and patchy fog. After daybreak, conditions are expected to improve to VFR with isolated to scattered showers. Light east-northeasterly winds will persist through the valid TAF period. EXTENDED OUTLOOK...Isolated to scattered convection, mainly during the afternoon and evening hours is possible beneath the cutoff upper low through Friday. MVFR/IFR morning stratus/fog possible each day through Saturday. Expect mainly VFR Sunday through Tuesday. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 1015 PM Thursday...This update mainly concerned with pcpn coverage during the pre-dawn Fri hours. The sfc and upper lows are situated along the NE South Carolina coast, and is slowly making some headway to the NE...and should reach the NC-SC border by daybreak Fri. Some very minor tweaks to wind direction applied due to the slower movement. In addition, the wrapping affect around the sfc low will continue overnight. Could see a few streamers ahead of the low, ie. Moving northward along Cape Fear and also onshore in the vicinity of Surf City or further northward along the coast into MHX CWA. Significant seas remain a solid 2 to 3 ft with majority coming from the ese ground swell at 11-13 second periods from distant Karl. Previous...................................................... As of 600 PM Thursday...A relatively relaxed sfc pg will yield 10 kt or less wind speeds tonight. The progged sfc pressure field itself paints the elongated sfc low, underneath the upper low, straddling the coasts of NC and SC thru tonight. Could go variable in direction especially with speeds only at 5 to 10 kt, but instead will identify the more predominate directions, southeast to south. Significant seas will primarily be driven by a 1.5 to 2.5 foot, e to ese ground swell from distant Tropical Cyclone Karl. Latest Spectral Density Chart for 41013 indicates the ese 11-13 second period Karl swell is definitely driving the significant seas. Have increased the convection coverage this evening based on latest KLTX 88D trends. In addition, have highlighted the persistent convection over the northern-most waters oriented parallel to Cape Fear, as it pushes northward and onshore. Waterspout(s) has/have been sighted earlier today in the vicinity of this pcpn. Will mention this waterspout risk until sunset in the Hazardous Weather Outlook. SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 300 PM Thursday...Low pressure just off the tip of Cape Fear will finally move away as high pressure builds down behind through Saturday. A cold front will drop south reaching NC Sat night and should move through the waters by Sun morning. This may be fairly transparent as winds will have already shifted to the N-NE by late Fri as low weakens and shifts east. Therefore light and variable winds on Fri will become northerly by early Sat and will remain N to NE through Sat night increasing up to 15 kts. Seas 3 ft or less will increase up to 2 to 4 ft into Sat night. A longer period SE-E swell will continue through the weekend, up to 11 to 12 seconds. LONG TERM /SUNDAY THROUGH MONDAY/... As of 300 AM Thursday...Surface high pressure will build down the eastern seaboard behind a cold front, which should be crossing the waters during the day Sunday. With a blocked upper-level pattern developing through the first of the week, the surface high will persist and result in onshore flow through Monday. It does still appear that 3-4 foot swells every 10 seconds will continue into Sunday from distant tropical system Karl, falling off to a 2-3 foot wind wave by Monday. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...DCH NEAR TERM...DCH SHORT TERM...RGZ LONG TERM...RGZ AVIATION...SGL
Area Forecast Discussion
National Weather Service Phoenix AZ
900 PM MST THU SEP 22 2016 .SYNOPSIS... Drier air and slightly cooler temperatures will be over the area for the remainder of the week. Breezy, but otherwise quiet weather will be the rule for the weekend and into early next week along with a warming trend. && .DISCUSSION... After an interesting afternoon in the Phoenix area with some fast- moving dynamic thunderstorm activity we are seeing things quieting down a lot. Humidity is still present with dew points in the high 60s and low 70s in the Phoenix area but have substantially dried out to the west, going into the 20s and 30s in the Imperial Valley and Colorado River valley. Some gusty winds are present and have led to some areas of blowing dust in southeast California. That activity should be diminishing this evening. The next few days should be relatively quiet with cooler dry air settling in over the region. Temperatures should stay below normal levels. By Sunday a cutoff low pressure system is forecast to cut off over southern NM. This will keep us in relatively cool northerly flow. One curiosity in the long range is yet another tropical system that at least one model (GFS) is bringing back up into the Baja/AZ area in a very similar track to Paine. That`s a pretty unusual track for very late in September but not out of the question. For now it`s just something to watch and see. A lot can happen in the next week. && .PREVIOUS DISCUSSION... Initial line of showers steadily dissipated as it tracked eastward across the Phoenix area early this afternoon. In its wake, more scattered but organized storms have developed across portions of western Maricopa County within a moist and unstable environment with dewpoints as high as the lower 70s yielding MLCAPEs exceeding 1000 J/kg. Meanwhile, NAEFS percentiles show a widespread area of anomalous PWATs, exceeding the 90th percentile across central AZ extending northward. Latest runs of the HRRR continue to have a good handle on the situation and indicate that additional activity will develop this afternoon before dissipating around 5pm. The strongest storms are expected generally to the north and west, where temperatures aloft are cooler and in the vicinity of the strongest deep-layer shear associated with the closed low across central California. Main threats include brief heavy rain, strong winds gusts and small hail. Otherwise, PoPs remain in the forecast overnight for southern Gila County. Global models continue to suggest strong vorticity-forced ascent ahead of the trough axis will tap into some residual moisture to generate scattered showers in these areas. && .PREVIOUS DISCUSSION... Gusty west winds are expected to develop over the western deserts this afternoon behind the front, with the strongest winds likely to occur over favored areas of Imperial county; peak gusts to 35 mph are likely. There may be some patchy blowing dust occurring due to the wind, but recent rains in the area will limit the potential for any significant dust and as such we will not mention blowing dust in our forecast grids at this time. As far as temperatures go today, with thickness values lowering to around 576dm and with considerable lower clouds and showers in the area, high temperatures will fall to well below seasonal normal values with many lower AZ deserts falling into the upper 80s to low 90s. Phoenix should see a high around 90 today which would be 8 degrees below normal. On Friday, the main upper low is forecast to quickly lift off to the northeast but a much drier and more subsident northwest flow aloft will overspread the deserts. Outside of a lingering slight chance of showers over southern Gila County we can expect generally sunny skies over the lower deserts with continued below seasonal normal high temperatures. PWAT values are forecast to fall to around one quarter of inch over much of the lower central deserts by Friday afternoon and the surface dewpoints in the Phoenix area will fall from the mid to upper 60s today into the upper teens to mid 20s. Over the weekend and into next week, dry conditions are forecast area wide with no threat of precipitation. A large upper ridge will initially amplify along the west coast giving a dry northerly flow to the area but early next week the ridge will flatten somewhat but continue giving dry northwest flow into the lower deserts. Expect generally sunny days and clear nights this weekend into the middle portion of next week along with a gradually warming trend. High temperatures will climb into the mid to upper 90s over most of the lower deserts by the early to middle part of next week. .AVIATION... South-Central Arizona Including KPHX, KIWA, and KSDL: Shower and thunderstorms continue to develop upstream of the Phoenix area terminals and all terminals stand a chance to see some precip activity through the evening hours. Airfield vsbys may take a sudden drop under the heaviest shower activity and resulting winds will also be on the rather variable and erratic side. Otherwise, CIGs will linger 3-5kft into the evening before transitioning eastward with FEW to SCT clouds lingering after sunset. Any continuing shower activity should move and stay east of the terminals for the overnight hours. Southeast California/Southwest Arizona including KIPL and KBLH: Breezy to windy conditions to persist for KIPL and KBLH as a cold front continues to pass through the region. Gusts 25 to 30kts will linger into the overnight, with sustained winds holding in the 10 to 15kt range. Skies will remain mostly clear with any shower activity remaining well to the east of the River and the terminals. Aviation Discussion not updated for amended TAFs. && .FIRE WEATHER... Saturday through Wednesday... Very dry northwesterly flow aloft behind a trough to the east on Saturday will eventually be replaced by a dry ridge of high pressure on Wednesday along with below normal high temperatures throughout the period. Breezy to occasionally windy northerly component winds will prevail out west, especially along the lower Colorado river valley each afternoon through Monday with gusts of 20 to 28 mph, although conditions are not expected to reach critical thresholds at this time. Gusty northeasterly winds will then spread into the lower deserts and the higher terrain of southern Gila county beginning Tuesday. Minimum RH of 13 to 20 percent on Saturday will slowly increase each day until reaching only 20 to 30 percent on Wednesday. Fair overnight recoveries on Saturday will improve to fair to good by Tuesday. && .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected through Sunday. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ Visit us on Facebook...Twitter...and at weather.gov/phoenix DISCUSSION...Waters/Hirsch PREVIOUS DISCUSSION...CB AVIATION...Nolte FIRE WEATHER...Sawtelle
Area Forecast Discussion
National Weather Service Las Vegas NV
826 PM PDT THU SEP 22 2016 .SYNOPSIS...Strong and gusty winds across San Bernardino County will diminish overnight as a strong area of low pressure moves east into Utah and Arizona. Scattered showers and thunderstorms over northern Mohave County will also come to an end. Below average temperatures are expected through the weekend, warming to near average early next week, with drier and calmer conditions anticipated. && .UPDATE...Wind speeds have diminished on schedule so let most of the products expire as scheduled. Did downgrade the High Wind Warning for the western Mojave Desert to a Wind Advisory and left the advisory up for the Morongo Basin as well. Heavy rain threat has ended for northern Mohave County so went ahead and cancelled the Flash Flood Watch a few hours early. Strong winds throughout the day lofted quite a bit of dust into the air. Visibilities locally being impacted by this suspended dust now so added a large swatch of haze to the high desert of San Bernardino County, Clark County and western Mohave County. Would expect the visibilities to gradually improve overnight and Friday as the dust settles out. && .AVIATION...For McCarran...Forecast confidence is low on the exact influence of a cold front this evening. Some forecast computer models are suggesting winds will struggle to become northwesterly and settle in a more westerly direction while others push through the front and bring northwest wind overnight. For now, the TAF will hint at a slight WNW direction overnight with a more gradual shift to NW overnight as winds subside. Mechanical turbulence and low level wind shear impacts will diminish overnight as winds subside. For the rest of southern Nevada...northwest Arizona...and southeast California...Chances of showers/storms confined to Mohave and Lincoln Counties today with strong west to southwest winds the main concern elsewhere. Cold front will move through the southern Great Basin and Inyo County this afternoon/evening with switchover to northwest directions during/after passage. Winds should diminish after sunset, but may be slower to occur in the Mojave Desert. VFR conditions outside of storms. Mechanical turbulence and mountain wave activity is anticipated through this evening. && .PREV UPDATE...554 PM PDT THU SEP 22 2016 .UPDATE...Increased POPs back westward into northeast Clark County/eastern Lake Mead National Recreation Area as new line of storms has developed from Temple Bar area northeast through Mesquite. A line of stronger storms continues to exist from north of Kingman to Colorado City. HRRR simulations have been consistent showing lines of convection weakening or moving out of Mohave County around 9 pm. Cold front making progress southeast and currently lies from Alamo-Desert Rock-Ridgecrest. Frontal passage for Las Vegas still looks to be around 8 pm. && .PREV DISCUSSION...242 PM PDT THU SEP 22 2016 .SHORT TERM...through tonight. WV imagery showing deep trough/upper low continuing to dig southeastward into the Great Basin this afternoon. Jet streak is approaching the base of the trough, with substantial difluence/divergence in eastern Nevada, Utah, and northern Arizona in favorable left front quadrant region. Substantial large-scale lift from differential cyclonic vorticity advection has reached the more unstable warm sector of far eastern Nevada SSE to western Arizona, and more intense updrafts have recently developed in Lincoln County southward to Lake Mead. High-resolution guidance is consistently showing a band or bands of storms developing in this general area moving eastward into southwest Utah and northern Mohave County over the next several hours. Environmental parameters remain favorable for storm organization, with effective bulk shear 30-40 kts and MUCAPE 500-1000 J/kg sufficient for isolated severe storms capable of producing damaging wind gusts. Though potential for hail exists, think the general weakness of the updrafts will not support a more widespread threat. Storm motions will be fast with such midlevel steering winds in place, but if sustained updrafts can develop in small bands or lines, training thunderstorms with efficient rain rates will be capable of producing localized flash flooding, especially with antecedent rains in northern Mohave County the last couple of days. Flash flood watch remains in effect for this area this evening. Winds look to remain strong as the trough axis approaches the area this evening, but a cold front sweeping through the southern Great Basin at this time will generate a switchover to northwest winds with speeds decreasing rapidly thereafter. Dust has been kicked up across the Mojave Desert this afternoon, with reduced visibilities reported along I-15 from Baker to Barstow. Expect blowing dust to remain a concern through sunset in this region before gradual improvement with lowered wind speeds thereafter. Current wind/dust products look good and did not change with the afternoon package. Red flag conditions are being met across much of the area this afternoon as well. See the fire weather discussion for more information. Sharply cooler temperatures are expected tonight as colder air behind the front seeps into the region. Expect temps anywhere from 7- 15 degrees colder than those observed last night. .LONG TERM...Friday through Thursday. A final shortwave over southern Nevada will be moving through the base of the vigorous trough early Friday morning. This will allow the upper trough to start moving eastward into the Four Corner States by late Friday afternoon. On backside of trough, temperatures will be much cooler Friday (around 10 degrees below normal) along with lingering north breezes. Over the weekend, southern extent of upper trough stalls over the southern Rockies as strong high pressure begins to build in across California/western Nevada. Daytime temperatures quickly rebound back to near normal Sunday. A developing north/south surface pressure gradient will help enhance north/northeast surface winds, especially within the Colorado River Valley south of Hoover Dam both days. More uncertainty next week as models continue to struggle with handling of southern stream energy pinching off over New Mexico. Quite a bit of flip-flopping between operational ECMWF/GFS runs as just last night`s solutions had back away from any energy retrograding westward across Arizona/northwest Mexico. Based on the strength of the ridge over California and the Great Basin, it is plausible. For now, keeping the area dry with temperatures hovering around normal. && .AVIATION...For McCarran...Southwest winds 20-30 kts with gusts to 40 kts will be likely through the afternoon. Forecast confidence is low on the exact influence of a cold front later this afternoon on winds at McCarran. Some forecast computer models are suggesting winds will struggle to become northwesterly and settle in a more westerly direction while others push through the front and bring northwest wind overnight. For now, the TAF will hint at a slight NW direction at 03z with a more gradual shift to NW overnight as winds subside. A plausible alternative to the official forecast is that we will see a sudden shift to the NW (~330) with strong gusty winds at around 03z. This should be considered in any planning during this period of time. Mechanical turbulence and low level wind shear will also remain a problem for the rest of the afternoon. For the rest of southern Nevada...northwest Arizona...and southeast California...Chances of showers/storms confined to Mohave and Lincoln Counties today with strong west to southwest winds the main concern elsewhere. Cold front will move through the southern Great Basin and Inyo County this afternoon/evening with switchover to northwest directions during/after passage. Winds should diminish after sunset, but may be slower to occur in the Mojave Desert. VFR conditions outside of storms. Mechanical turbulence and mountain wave activity is anticipated through this evening. && .FIRE WEATHER...Much drier air has arrived with relative humidity values plummeting into the single digits along with strong southwest to west winds. Winds will start to weaken by late evening as relative humidity values recover above 15 percent overnight as temperatures cool. North to northeast breezes will continue at times Friday through Sunday as high pressure builds in across California and the Great Basin. Temperatures will be well below Friday but will warm through the weekend. && .SPOTTER INFORMATION STATEMENT...Spotters in northwest Arizona are encouraged to report severe weather or flooding. Spotters elsewhere can report significant weather (especially blowing dust, wind damage, or fire starts) according to standard operating procedures. && $$ Update...Pierce Short Term:Shafer Long Term/Fire Weather:Pierce Aviation: Lericos For more forecast information...see us on our webpage: http://weather.gov/lasvegas or follow us on Facebook and Twitter
Area Forecast Discussion
National Weather Service Cheyenne WY
326 AM MDT FRI SEP 23 2016 .SHORT TERM...(Today through Saturday) Issued at 310 AM MDT Fri Sep 23 2016 Widespread low clouds continue across areas along and east of the Laramie Range. WYDOT obs from Cheyenne to the I-80 summit show vis remaining mostly below a quarter mile so the dense fog advisory is working out well. Will keep it going for central Laramie county even though the fog has not developed at CYS yet. HRRR guidance shows much quicker clearing through the morning compared to yesterday. Models show the closed upper low currently near Salt Lake City lifting northward into central WY by this evening. The warm front will lift northward across the plains through the day with southerly winds strengthening from I-25 eastward. Did increase wind speeds over the Panhandle with the southern Panhandle getting close to advisory level (fcst gusts to 35 kts) by the late aftn. Cold front is progged to be near the Laramie Range by the aftn, and this will be focus for shower/tstm development. Went with 40-60 POPs over much of the plains of southeast WY during the aftn as the HRRR/NCAR ensembles are in good agreement with the global models. There will be a marginal risk of svr storms across the plains and especially north of the warm front. This is due to CAPE values of 500-1000 J/kg and excellent bulk shear. Storm activity over the plains should begin to die down by the late evening with the cold front pushing across the Panhandle by 06Z. The other story with this storm system will be the orographic snow over the Sierra Madre and Snowy Ranges by late tonight into Saturday morning. Wet bulb zero heights are around 8500 ft MSL. Moist westerly 700-500 mb flow on the backside of the upper low will create favorable orographics, especially over the Sierra Madre Range. Currently have 1-4 inches of snow over much of the western mtns, which would be welcome news for the fires that have been ongoing near the Sierra Madre Range. It will be breezy to windy on Saturday with highs struggling to get above the mid 60s. .LONG TERM...(Saturday night through Thursday) Issued at 310 AM MDT Fri Sep 23 2016 Upper trough moves through the area Saturday night into Sunday. Going to be cold as 700mb temperatures fall to -4C Sunday into Monday. Warmer and drier weather for the rest of the upcoming week as ridge of high pressure builds back over the area. && .AVIATION...(For the 06Z TAFS through 06Z Friday night) Issued at 1105 PM MDT Thu Sep 22 2016 Challenging forecast for the overnight hours. HRRR guidance showing IFR/LIFR lifting across the southern Panhandle early this morning as a trough of low pressure moves out of northeast Colorado. Generally followed the HRRR guidance on timing/clearing of stratus and fog. Strong winds this afternoon and evening as a cold front moves through the area. Could see gusts to 45kts out at KSNY, KAIA and KBFF, first from the southwest and then from the northwest when the front moves through. && .FIRE WEATHER... Issued at 310 AM MDT Fri Sep 23 2016 No fire weather concerns through the weekend. Temperatures will cool across the entire area after today behind a cold front. Minimum afternoon humidity values will mostly be above 25 percent through the weekend. There will be a chance of showers and thunderstorms through tonight across the region. A few inches of snow will be possible tonight through Saturday morning over the Sierra Madre and Snowy Ranges. && .CYS Watches/Warnings/Advisories... WY...Dense Fog Advisory until 7 AM MDT this morning for WYZ116>118. NE...None. && $$ SHORT TERM...ZF LONG TERM...GCC AVIATION...GCC FIRE WEATHER...ZF
Area Forecast Discussion
National Weather Service Tucson AZ
920 PM MST THU SEP 22 2016 .SYNOPSIS...A strong low pressure system moving north of the area will bring a chance of showers and/or thunderstorms, cooler temperatures and gusty winds at times through Friday. Mostly dry conditions will then prevail this weekend and into the latter part of next week. && .DISCUSSION...Showers and a few thunderstorms associated with the tail end of a low pressure system passing through the Great Basin had dissipated late this evening. Latest HRRR solution continued to suggest the possibility of a flare up in showers late tonight and more so Friday afternoon mainly northeast of Tucson. The current forecast resembled this solution which still looked plausible. Thus, no updates anticipated this evening. Please refer to the additional sections for more details. && .AVIATION...Valid through 24/06Z. A few showers and/or thunderstorms will continue mainly from the Tucson area north and westward as a cold front slowly moves through the area into Friday. Expect a band of SCT-BKN clouds at 3-7 ft AGL to gradually make its way across the region from west to east as well. Surface wind becoming terrain driven less than 10 kts overnight. Breezy westerly to southwesterly winds are expected again Friday afternoon. && .FIRE WEATHER...Isolated showers and storms are possible through tonight and again on Friday, especially from Tucson north and westward as a cold front moves across the area. Southwest winds of 10-15 mph and occasional 20 mph gusts will subside this evening. A few west to southwest breezes on Friday will continue for eastern areas. Otherwise, mainly light winds this weekend before increased easterly breezes move in for much of next week. Minimum relative humidity values will begin to lower considerably as early as Friday for far western areas, then for the remainder of the region this weekend into early next week. && .PREV DISCUSSION...A low pressure system was moving through the Great Basin region this evening. A small threat for showers will linger through Friday before the system moves generally over the northern Rockies with the tail end of the system into the four corners region by late Friday. As this system swings through, the associated cold front will result in a significant decrease in temperatures with highs only expected to be in the mid to upper 80s for Tucson during the entire forecast period. The trough axis associated with the aforementioned low pressure system will linger just to our east into the weekend before an upstream vort max dives south on the back side of the trough across eastern Utah and Arizona Saturday into Sunday. As this occurs, models are showing some significant differences beyond Sunday. The ECMWF wants to develop a cut-off low over the general vicinity of southeast Arizona, southwest New Mexico, northeast Sonora and northwest Chihuahua on Sunday, while the GFS just keeps the trough to our east over northeast New Mexico through west Texas and northern Chihuahua. By late Monday the Euro indicates the low will retrograde over northern Sonora, while the GFS has the tail end of the trough sliding farther south into north central Mexico. Meanwhile, the models develop a tropical system near the equatorial Pacific and the GFS eventually takes it to the north and it becomes absorbed into the low over southern Baja by the middle to latter part of next week and moves this whole system northward. On the other hand, the Euro takes the low over Sonora and moves it northwest to a position over western Arizona by mid week, but then kicks it east in response to an upstream trough. The bottom line is that during the early to latter part of next week, the Euro starts out wet and then becomes dry, whereas the GFS starts the week out dry and then ends it wet. So, with this much uncertainty I just have single digit to slight chance type POPs in the grids/forecast until models can come to some consensus. For Tucson, high temperatures will be 8 to 10 degs below normal Friday, then will range from 3 to 6 degs below normal each day thereafter, although the coolest days will be Saturday through Tuesday. Low temps will be near normal Friday morning, then 6 to 8 degs below normal this weekend and within a degree or two of normal thereafter. && .TWC WATCHES/WARNINGS/ADVISORIES...None. && $$ Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson
Area Forecast Discussion
National Weather Service Bismarck ND
1001 AM CDT Fri Sep 23 2016 .UPDATE... Issued at 950 AM CDT Fri Sep 23 2016 The biggest change with this update is associated with the expansion of the SPC Day 1 Marginal Risk into a great portion of southwest North Dakota with their 13 UTC outlook. The 11-14 UTC HRRR iterations and the experimental ESRL HRRR within their 2-5km updraft helicity forecasts have consistently shown tracks of 75-100+ m2/s2 across southwest North Dakota this evening, pointing to the potential for organized convection. This is plausible given increasing low level warm air advection and moisture transport arching into the southwest north of the surface low that will be propagating into western South Dakota and Nebraska, coincident with the next surge of upper level forcing. 850mb CAPE values around 1000 j/kg in a highly sheared environment suggest low topped supercells could be possible. Large hail is the most likely threat given the likely elevated nature of the storms. UPDATE Issued at 632 AM CDT Fri Sep 23 2016 For this update, no major changes were needed. Tweaked the temperatures through the morning hours as well as the QPF forecast. Otherwise, just blended the most current observations to the inherited forecast. Decided to keep precipitation chances as is for the time being, as showers should continue to become more numerous over western and central North Dakota through the morning and afternoon hours. Once the surface low begins to mature over South Dakota, should have a better idea of eventual coverage by later this afternoon. Isolated thunder is still expected with the activity today, mainly in the south. Severe weather is not expected at this time. Stronger shortwave approaches tonight, bringing more widespread rain and thunderstorm potential to the west as the low lifts into North Dakota. && .SHORT TERM...(Today through Saturday) Issued at 515 AM CDT Fri Sep 23 2016 This Friday morning the mid level low, that began impacting our weather with an increase in clouds yesterday, was over Utah and progged to move northeast. This is consistent model to model. By Saturday afternoon it is either over eastern Montana or western North Dakota, depending on which model is followed, and ends up in Manitoba by Sunday. The 150 mile difference in track of that mid level low results in very little difference in sensible weather as the surface low track is much more in line model to model. Basically what this track and diffluent flow aloft means is a lot of clouds and numerous showers. It also means warmer weather ahead of the surface feature as winds veer to southerly, and an increase in instability. We`d also expect a dry slot to work in, likely through the central Dakotas, resulting in some sunshine on Saturday. The surface low track and tightening gradient would support windy weather Saturday and Sunday, very windy southwest with an advisory possibly needed. As far as lightning, the better chances are along and south of I-94 as CAPE and instability are highest, but still not impressive, later today. storms could fire in the dry slot Saturday, and conditions would favor strong storms, but they would likely form in the central Dakotas, strengthening as they move east. .LONG TERM...(Saturday night through Thursday) Issued at 438 AM CDT Fri Sep 23 2016 Gusty wind in the wake of the low continues for Sunday, again, possibly advisory levels. Behind the mid level low on monday we`d typically expect cooler air, however, models agree on strong H5 ridging, in response to the deepening low, into the forecast area. This means back to normal, and even above normal temperatures, to end September. && .AVIATION...(For the 12Z TAFS through 12Z Saturday morning) Issued at 950 AM CDT Fri Sep 23 2016 Widespread IFR/MVFR conditions in stratus, rain showers and thunderstorms are forecast across western and central North Dakota today and tonight. A brief improvement to VFR is possible at KBIS Saturday morning as dry air works into the storm system impacting the area. && .BIS WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...AYD SHORT TERM...JPM LONG TERM...JPM AVIATION...AYD
Area Forecast Discussion
National Weather Service Cheyenne WY
522 AM MDT FRI SEP 23 2016 .SHORT TERM...(Today through Saturday) Issued at 310 AM MDT Fri Sep 23 2016 Widespread low clouds continue across areas along and east of the Laramie Range. WYDOT obs from Cheyenne to the I-80 summit show vis remaining mostly below a quarter mile so the dense fog advisory is working out well. Will keep it going for central Laramie county even though the fog has not developed at CYS yet. HRRR guidance shows much quicker clearing through the morning compared to yesterday. Models show the closed upper low currently near Salt Lake City lifting northward into central WY by this evening. The warm front will lift northward across the plains through the day with southerly winds strengthening from I-25 eastward. Did increase wind speeds over the Panhandle with the southern Panhandle getting close to advisory level (fcst gusts to 35 kts) by the late aftn. Cold front is progged to be near the Laramie Range by the aftn, and this will be focus for shower/tstm development. Went with 40-60 POPs over much of the plains of southeast WY during the aftn as the HRRR/NCAR ensembles are in good agreement with the global models. There will be a marginal risk of svr storms across the plains and especially north of the warm front. This is due to CAPE values of 500-1000 J/kg and excellent bulk shear. Storm activity over the plains should begin to die down by the late evening with the cold front pushing across the Panhandle by 06Z. The other story with this storm system will be the orographic snow over the Sierra Madre and Snowy Ranges by late tonight into Saturday morning. Wet bulb zero heights are around 8500 ft MSL. Moist westerly 700-500 mb flow on the backside of the upper low will create favorable orographics, especially over the Sierra Madre Range. Currently have 1-4 inches of snow over much of the western mtns, which would be welcome news for the fires that have been ongoing near the Sierra Madre Range. It will be breezy to windy on Saturday with highs struggling to get above the mid 60s. .LONG TERM...(Saturday night through Thursday) Issued at 310 AM MDT Fri Sep 23 2016 Upper trough moves through the area Saturday night into Sunday. Going to be cold as 700mb temperatures fall to -4C Sunday into Monday. Warmer and drier weather for the rest of the upcoming week as ridge of high pressure builds back over the area. && .AVIATION...(For the 12Z TAFS through 12Z Saturday morning) Issued at 519 AM MDT Fri Sep 23 2016 Looks like the HRRR guidance is maybe an hour fast on lifting ceilings out in the Panhandle. So adjusted the forecast some to continue low clouds out that way through the morning hours. Looks like most areas should be VFR by 15-16Z or so. Still looking windy this afternoon with the approach of the cold front with LAMP guidance still showing wind gusts to 40kts for our Panhandle airports. && .FIRE WEATHER... Issued at 310 AM MDT Fri Sep 23 2016 No fire weather concerns through the weekend. Temperatures will cool across the entire area after today behind a cold front. Minimum afternoon humidity values will mostly be above 25 percent through the weekend. There will be a chance of showers and thunderstorms through tonight across the region. A few inches of snow will be possible tonight through Saturday morning over the Sierra Madre and Snowy Ranges. && .CYS Watches/Warnings/Advisories... WY...Dense Fog Advisory until 7 AM MDT this morning for WYZ116>118. NE...None. && $$ SHORT TERM...ZF LONG TERM...GCC AVIATION...GCC FIRE WEATHER...ZF
Area Forecast Discussion
National Weather Service Bismarck ND
309 PM CDT Fri Sep 23 2016 .SHORT TERM...(This evening through Saturday) Issued at 248 PM CDT Fri Sep 23 2016 Severe thunderstorm potential southwest this evening and tonight highlights the short term forecast. The 15-18 UTC operational and experimental HRRR iterations continue to show strong run to run consistency in developing convection across eastern Wyoming this afternoon, and propagating this convection into southwest North Dakota by 02-04 UTC, sustained by a strengthening low level jet and a resurgence of upper level forcing ejecting out of the intermountain west upper level low. This is supported by the greater 12 UTC CAM suite. These HRRR iterations continue to depict in their 2-5 km updraft helicity fields tracks of 75-100+ m2/s2 across southwest North Dakota, supporting the potential for organized convection possibly in the form of elevated low topped supercells to survive from Wyoming into southwest North Dakota. Large hail and damaging winds are the primary threats given the likely elevated nature of these storms. For Saturday, followed a blend of the 12 UTC global suite given good agreement amongst the larger scale guidance for the aforementioned upper level low to propagate into southwest North Dakota by early Saturday evening. A dry slot is favored across much of the south central for Saturday, with wrap around stratiform precipitation across the far west, and potentially more convective precipitation across the north central and James River Valley. .LONG TERM...(Saturday night through Friday) Issued at 248 PM CDT Fri Sep 23 2016 Strong winds across the west Saturday night with a dry forecast for the remainder of the period thereafter highlight the extended forecast. Given good agreement, followed a blend of the 12 UTC global guidance suites for most fields. The nearly stacked low from the short term is forecast to propagate across North Dakota Saturday night. All ingredients will be available for strong winds on the backside of the low, with a tight pressure gradient and strong cold air advection aided by isallobaric forcing. 0.5 km winds around 50 kts are forecast across the west, which will have to be monitored for the next few models runs should a high wind watch become necessary across the west for Saturday night into Sunday. Thereafter, broad upper level ridging builds across the central CONUS Tuesday through the remainder of next week, signaling a drier pattern with near to slightly above average temperatures. && .AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon) Issued at 248 PM CDT Fri Sep 23 2016 Widespread IFR/MVFR conditions in stratus, fog, rain showers and thunderstorms are forecast across western and central North Dakota today and tonight. A brief improvement to VFR is possible at KBIS/KJMS late tonight into Saturday morning as dry air works into the storm system impacting the area. && .BIS WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...AYD LONG TERM...AYD AVIATION...AYD
Area Forecast Discussion
National Weather Service Taunton MA
410 PM EDT Fri Sep 23 2016 .SYNOPSIS... A cold front will cross the region this evening, bringing lower temperatures. A band of rain showers is also expected behind this front later this evening into tonight, but amounts will be light. Cool and dry weather will follow this weekend into early next week. A slow-moving low pressure and cold front could lead to some showers late next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... Latest mesoanalysis continues to show a very unfavorable environment for supporting thunderstorms across southern New England. Abundant clouds, as well as a stout low level inversion, from earlier today has limited our warm up. More sunshine developing across southern New England this afternoon. But it may be a case of too little, too late. Looking upstream, lots of lower clouds behind a cold front across southern VT and NH. That indicates more abundant moisture, and the possibility of some showers. Short-term guidance, such as the HRRR and RAP, continues to indicate a higher likelihood of at least some lightly measuring showers. Will continue with a brief period of chance PoPs this evening. Only moderate confidence rainfall chances will actually be as high as suggested by the guidance with few radar returns upstream, despite the run-to-run consistency of the guidance. Band of rain showers will continue to press from north to south with band of mid level frontogenesis/moisture behind a cold front. Much cooler air will continue to work into the region tonight and northeast winds will be a bit gusty along the coast. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Drier air will move in from the northwest, allowing for skies to become mostly sunny during the morning. Mostly clear skies continue through Saturday night. Below normal temperatures during this time as well. If winds can diminish enough, there is the remote possibility of some frost across portions of the east slopes of the Berkshires Saturday night, particularly in Franklin county. Will need to monitor this, but think it is a low probability event at this time. However, a fall-like atmosphere will be in place with 850T between +3C and +5C. High temps should still recover well into the 60s to near 70 given lots of sunshine, but certainly be our first true taste of early fall. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Highlights... * Dry and cool weather continues through Monday with patchy frost possible for some locations Sunday night. * Precipitation chances increase Monday night thru Wednesday night, with a return to seasonable temperatures. Overview and model preferences... Omega block over the Mississippi Valley continues to translate east and gradually deamplify through the middle of the upcoming week. The 23/12Z model suite begins to diverge around 12Z Monday, with the ECMWF notably weaker, and thus more progressive, with its handling of the closed low over the Great Lakes. We leaned toward the slower and more amplified GFS solution, given the interaction of several pieces of energy, as the ECMWF may be breaking down the block too quickly. But confidence in the details is below average, and will remain so, until the models better resolve competing shortwave energy interacting with the closed low. Details... Sunday and Monday... Northwest flow aloft will keep the region dry during this time frame, as Canadian high pressure crests across the region by Monday morning. Given the combo of a dry airmass in place, as well as a decoupled boundary layer, we anticipate ideal radiational cooling conditions to occur Sunday night. Thus, we went below guidance on temperatures, which may bottom out in the low to mid 30s for portions of the region. In particular, the interior locations northwest of the Mass Pike and I-495, as well as interior southeast Massachusetts, have the potential for their first frost of the season. Otherwise, there will be an increase in mid and high level cloudiness on Monday, as a warm front approaches the region. Monday night thru Wednesday... There is still uncertainty with the timing of a cold front during this time frame, with the more progressive ECMWF keying in on Tuesday morning, while the GFS holds off until Wednesday afternoon. We leaned more toward the GFS, and focused PoPs in the Monday night to Wednesday morning period. We also kept consistency with the previous forecast, with the greatest chance of precip focused in the late Tuesday thru early Wednesday time frame, when the deepest moisture and strongest dynamics coincide. This system does not have much in the way of moisture to work with, as Precipitable Water values only rise to 1.5 inches, so rainfall will be generally light. We also cannot rule out a rumble of thunder along the south coast Monday night into early Tuesday, as some elevated instability traverses this area. Thu and Fri... Still some uncertainty regarding how quickly the upper low departs the region. We maintained NIL to low PoPs, especially considering the amount of moisture along the back side of this feature. && .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Tonight...Moderate to high confidence. A period of MVFR CIGS in a band of showers are likely behind a cold front. Northeast wind gusts of 20 to 25 knots expected along the coast. Saturday...High confidence. Mainly VFR. Any leftover MVFR Cigs, and perhaps some patchy early morning fog in the typical locations, will improve to VFR by mid morning. Saturday night...High confidence. VFR. KBOS TAF...Moderate confidence in TAF due to shower coverage. High confidence in winds. Wind shift to the northeast with brief gusts to 25 kt possible between 23/20Z and 24/06Z, along with a period of MVFR CIGS and showers. KBDL TAF...Moderate confidence in TAF due to shower coverage. High confidence in winds. Outlook /Sunday through Wednesday/... Sun thru Mon...High confidence. Predominantly VFR. Northwest winds may gust to 25 kt near shore on Sunday. Mon night thru Wed...Moderate confidence. Localized MVFR conditions possible in showers, mainly Tue night into Wed, with uncertainty with regard to timing. Otherwise VFR. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Tonight...High confidence. A strong cold front should result in a period of northeast wind gusts up to 25 knots, and 3 to 6 foot seas across our open waters, early this evening into the overnight hours. Small craft headlines posted for all waters except Narragansett Bay. Saturday into Saturday night...High confidence. Leftover 25 kt wind gusts diminish by mid morning as pressure gradient weakens. However, small craft headlines will continue across our outer waters into mid afternoon from leftover swell. These seas should finally drop below small craft advisory thresholds by late afternoon. Increasing north to northwest winds with a stronger surge of colder air over the waters. Not confident there will be a long period of sub advisory winds. So, will continue the small craft advisory into Saturday night across the outer coastal waters. Outlook /Sunday through Wednesday/... Sunday and Sunday night...High confidence. Small craft advisory conditions prevail. Northwest wind gusts around 25 knots Sunday, with seas 5 to 6 feet expected into Sunday night. Monday... Conditions are expected to remain below Small Craft Advisory criteria with high pressure building over the waters. Monday night thru Wednesday... An approaching storm system will lead to a period of southerly flow over the waters during this time frame. Small Craft Advisory criteria is possible during this period, however, the timing is uncertain. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 8 PM this evening to 8 AM EDT Saturday for ANZ231>235-237. Small Craft Advisory until 11 PM EDT this evening for ANZ230. Small Craft Advisory until 6 AM EDT Sunday for ANZ250. Small Craft Advisory until 8 AM EDT Saturday for ANZ251. Small Craft Advisory from 8 PM this evening to 6 AM EDT Sunday for ANZ254>256. && $$ SYNOPSIS...Belk/Franck NEAR TERM...Belk SHORT TERM...Belk LONG TERM...Franck AVIATION...Belk/Franck MARINE...Belk/Franck
Area Forecast Discussion
National Weather Service Gray ME
531 PM EDT Fri Sep 23 2016 .SYNOPSIS... Showers will continue along a cold front through this evening over southern New Hampshire and far southwestern Maine before much cooler and drier air arrives for the weekend as Canadian high pressure builds into the region. This will bring the potential for frost or freezing conditions Saturday and Sunday nights... especially over northern areas. Gradually moderating temperatures are expected Monday before another approaching cold front brings the threat for showers on Tuesday. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... 530 PM Update...Have updated the grids for the next few hours based on latest trends in observations and mesoscale model guidance. The result was little change to the going forecast. However, we did tighten up the PoP gradient a little bit across srn NH for this evening based on latest radar mosaic loops and HRRR guidance. Narrow stripe of showers is beginning to take shape across Upstate NY to the NW of ALB. This area of showers is expected to mainly affect Cheshire and Hillsborough counties this evening. Previous discussion... High Impact Weather Potential: Patchy frost in the far northern valleys possible. Current Pattern: Water vapor imagery early this afternoon shows an onslaught of northwesterly flow extending from Manitoba south and east to a leading shortwave now pressing through New England. This shortwave is interacting with a modest /although thinning/ moisture plume along the east coast to produce multiple bands of showers as it pushes south and east. Also of interest is an area of darkening in water vapor imagery over western Ontario which represents another upstream shortwave that will sharpen as it rapidly pushes southeast into New England during the first half of the night. Beyond this...sprawling 1030mb high pressure over northern Ontario will begin to push toward the region...bringing a clearing/drying/ cooling trend to the area. Forecast concerns are thus focused on precipitation potential through this evening...and temperatures as the continental polar airmass arrives tonight. Through Early Evening: Shower activity has dwindled markedly over the past 1-2 hours...so through 6pm expect little more than a few sprinkles/very light rain showers over southern areas with some breaks in the clouds opening up over northern areas. Tonight: High resolution near term guidance consensus has been honing in on another period of more widespread shower activity over southern NH and far southwestern ME this evening as aforementioned shortwave over Ontario sharpens and interacts with H8 frontal zone. The best window of opportunity for rain looks to be between 8pm and midnight...generally south of a LEB-PWM line. This will certainly help to boost meager rainfall totals in these areas thus far...with another few tenths of an inch of rain quite possible. Beyond this...cold and dry advection will be the rule with gradual clearing from north to south as PWATs retreat back below 0.5". Temperatures will fall rapidly...particularly with partial clearing after midnight...with consensus lows in the upper 30s north to mid/upper 40s south looking reasonable. Can/t rule out a few patches of frost over the far north...but not widespread /or confident/ enough to warrant a county-based headline. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... High Impact Weather Potential: Frost/Freeze Potential Saturday Night. Pattern: The short term forecast period will be dominated by continued northwesterly flow aloft given highly amplified trough/ridge/trough pattern across North America...with large surface high over eastern Ontario Saturday morning remaining nearly stationary through this forecast period. T8s start the period near the freezing mark...and gradually settle lower by Saturday night with these values representing -1 to -2 sigma departures from climatology. PWATs will similarly be in the -1 to -2 sigma range...promising little in the way of sensible weather through the period. Forecast concerns will center around temperatures Saturday night as the coolest night of the early fall season is expected. Saturday: Longwave trough will continue to deepen along the east coast of NOAM as sharp longwave ridging over the central portion of the continent slowly builds and moves east. This will maintain northwesterly flow through the column over our region...although any significant cool advection will be over by daybreak. BUFKIT profiles agree with CU rule suggestions from the guidance indicating some SCT cumulus development in the mountains...with very little in the way of cloudiness making it to the coast. So...expect a mostly sunny day for most spots. T8s will only be around +1-3C...so expect northern areas to remain in the 50s...with areas south of the mountains to reach the lower/middle 60s. Given the robust gradient aloft...expect northwesterly winds 10-20kts for the day...adding a bit of chill to the air. Saturday Night: High pressure remains north and west of the area with PWATs falling to around 0.25" in continental polar airmass. Expect any afternoon cumulus to clear...with a chilly night in store across the region. Primary factor potentially limiting the chill will be an ongoing breeze as 1000mb geostrophic winds remain 20-30kts overnight likely keeping many locations coupled. Honestly...this looks more like a freeze vs. no freeze situation with perhaps too much wind to support frost. Given the breeze...have kept overnight lows a bit higher than statistical guidance. Breeze will also restrict widespread fog...but given how cool temperatures will be...some CT valley locations will still probably see some patches. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Chance of High Impact Weather: Minimal. Where for the last few months 500mb blocking was hard to come by south of 50 N, we are finally starting to see sow blocks develop that will bring troughs down in the 30-40 N range. The models do not show stable blocking, but it is enough to bring temps to around normal with some fluctuations either side of normal through the long range. However, with the instability of the blocking, systems will be mobile and not very strong, so any chance for a soaking rain remains low through next week. The cold air will continue to stream in Sunday, as 500 mb trough works through in the morning. this air is very dry, but should produce some clouds in the mountains Sunday, maybe become mostly cloudy for a few hours. The coastal plain will see more sun in the downslope as N-NW winds pick up in the 10-20 mph with some higher gusts. Highs will be cool, and a few degrees below normal ranging from the low to mid 50s in the mountains to the low 60s in srn NH and along the ME coast. Sunday night will turn out to be an very good rad cooling night as sfc high builds in ands winds die off quickly with clearing skies. Lows will range from the mid-upper 30s in the mountains to the low 40s along the coast and in urban areas of the Merrimack valley. This will bring the threat of frost to almost everywhereexcept the immediate coast. Light winds shift to the SW on Monday as the high shifts offshore and it looks to be mainly a sunny day with highs a few degrees warmer than Sunday, bring temps to around normal, generally in the 60s. The next chance for rain will be in the Mon night thru Wed time frame as 500mb closed low tracks NE out of the great lakes and drags a cold front across the region. The Euro is a little progressive the fropa, ad moving the rain out by Tue night, with the GFS lingering it. However, the Euro also merges the two closed 500 lows to our north and spins the resultant low back SW and brings it just N of ME. This would result in cooler temps late in the week than the GFS. Went with Superblend, which split the difference which keeps temps around normal Wed-Fri, though if the Euro is right, they would be cooler, and if the GFS they would be warmer. && .AVIATION /22Z FRIDAY THROUGH WEDNESDAY/... Short Term... Summary: A cold front will push south of the region this evening with high pressure building in it/s wake through Saturday and remaining over the region through Saturday night. Restrictions: Band of showers will bring MVFR restrictions northern terminals...with CON/MHT/PWM/RKD likely seeing brief drops to MVFR. Conditions improve to VFR as showers depart this evening...with LIFR/IFR fog likely HIE/LEB...and possible CON/AUG. VFR for Saturday / Saturday night with the exception again being overnight fog HIE/LEB. Winds: Northwesterly winds 10g16kts this afternoon will diminish to 5-10kts /light and variable in the valleys/ for the overnight before increasing to 12g20kts from the northwest for the day Saturday. Northwest winds will diminish to below 10kts again Saturday night. LLWS: No LLWS expected through Saturday night. Thunder: Very slight chance of thunder MHT through 21UTC...but chance not great enough to mention in TAF. No thunder beyond this through Saturday night. Long Term...Sunday could continue to some N-NW wind gusts in the 20-25 kt range, but VFR Expected Sun-Mon. Some showers are possible Tuesday and Tue night, and could see a period of flight restrictions ahead of cold front Tue afternoon and night. && .MARINE... Short Term...Strengthening northerly winds tonight will bring winds/seas close to marginal SCA values for the overnight before shifting northwest on Saturday...with winds/waves remaining near marginal SCA values through Saturday night...after a brief lull in the winds early Saturday. Long Term...Borderline SCA possible Sunday in N-NW winds, but winds diminish by Sunday evening and stay below SCA through Wed. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory until 6 AM EDT Saturday for ANZ150-152- 154. && $$ SYNOPSIS...Arnott NEAR TERM UPDATE...Ekster SHORT TERM...Arnott LONG TERM...Cempa AVIATION...Arnott/Cempa MARINE...Arnott/Cempa
Area Forecast Discussion
National Weather Service Lincoln IL
310 PM CDT FRI SEP 23 2016 .SHORT TERM...(This evening through Saturday) ISSUED AT 310 PM CDT Fri Sep 23 2016 A surface boundary/back door cold front just south of I-74 this afternoon will continue to slowly sag sw across central IL into tonight, with 1029 mb surface high pressure over Ontario ridging into the Great Lakes region. Latest run of HRRR is now showing some convection from I-74 northeast late this afternoon and early evening but feel its coverage is too high and earlier runs of HRRR were dry. Current radar mosaic shows just isolated very light showers ne of Vermilion county IL which latest RUC model shows, so will keep pops at 10% over northeast CWA through 00Z/7 pm today. Dewpoints in the 60s across CWA and models show some increasing low level moisture near and northeast of the front tonight especially overnight into early Saturday morning allowing patchy fog to form with light wind regime. The latest forecast models continue to have a strong upper level ridge over IL on Saturday with 500 mb heights around 589 dm. This should bring another very warm summerlike day to the area with highs 85-90F and dewpoints in the mid to upper 60s. && .LONG TERM...(Saturday night through Friday) ISSUED AT 310 PM CDT Fri Sep 23 2016 The main focus for this forecast cycle will be the frontal passage and associated precipitation for this weekend. The 12z models seem to have better agreement on the a more progressive theme to the upper level pattern progression. The Canadian NH no longer cuts off a low behind the front, for later passage mid-week. The consensus indicates the occluded surface and upper low pressure centers will move from the western Dakotas Saturday afternoon northeast into Manitoba and western Ontario by Sunday evening. Then the upper trough is projected to deepen toward the southeast, into the central Great Lakes region. This will provide the reinforcing push of cooler air for our mid-week cool down. As for the sensible weather during this scenario, we are looking for increasing clouds Saturday night as the cold front moves half way across Iowa. We included a narrow ribbon of slight chance PoPs along our far western counties in Knox, Fulton and Schuyler counties. The strongest forcing for precip will generally remain north of our forecast area on Sunday as the surface and upper lows lift into western Ontario. As a result, the front circulation and low level moisture convergence will most likely be weakening during FROPA Sunday afternoon and early evening. Support for any thunderstorms will come from high boundary layer moisture with dewpoints around 70 in the pre-frontal air mass. Instability params will support a line of storms, with MUCAPES of 1500-2200 J/kg Sunday afternoon. Bulk shear will be marginal, in the 20-25kt range. The better agreement on frontal timing has increased confidence in precip on Sunday afternoon/eve, and PoPs were increased to Likely /60-70%/ north of I-72, progressing from west to east between Noon and midnight. Precip chances will linger into Monday as a secondary lobe of energy rotates through the upper trough before it departs to the east on Tuesday. A much cooler and drier air mass will settle into Illinois for Tuesday through Thursday. Highs will be below normal in the low 70s on Tuesday, then warm to near normal in the mid to upper 70s for Thursday, with upper 70s across the board on Friday. No precipitation is expected from Monday night through Friday, and possibly into next weekend. && .AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon) Issued at 1253 PM CDT Fri Sep 23 2016 VFR conditions will continue through this evening across the central IL airports with scattered cumulus clouds of 4-7k ft and scattered to broken cirrus clouds. A frontal boundary just south of PIA and BMI will push south of I-72 during this afternoon with light and variable winds becoming more ENE and staying less than 10 kts. Some fog could develop during overnight and bring MVFR conditions and possibly as low as IFR between 08Z-14Z. Strong upper level ridge building over IL during the next 24 hours will keep it dry. && .ILX Watches/Warnings/Advisories... NONE. && $$ SHORT TERM...07 LONG TERM...Shimon AVIATION...07
Area Forecast Discussion
National Weather Service Indianapolis IN
700 PM EDT FRI SEP 23 2016 .UPDATE... The AVIATION section has been updated below. && .SYNOPSIS... Issued at 141 PM EDT Fri Sep 23 2016 A large ridge of High Pressure over the plains states is expected to build across the Ohio valley and Great Lakes Tonight and Saturday. Meanwhile...High pressure over Ontario will also build southwest...providing dry but warm temperatures for central; Indiana this weekend. The upper ridge will moves east of Indiana by Sunday night...allowing a Cold front to approach the area for Sunday night and Monday. This will be the next best chance for showers or storms as this front passes early next week. Cooler High pressure in the wake of the front is expected to arrive by the middle of the next work week. This will lead to more seasonable temperatures then. && .NEAR TERM /Tonight/... Issued at 141 PM EDT Fri Sep 23 2016 Surface analysis early this afternoon shows broad high pressure in place across the Ohio Valley. A back door cold front was found from Western NY to NW Ohio...across NRN Indiana to Iowa. A few showers were found on the north side of this front. Wind fields here show well defined northeast surface flow in the wake of the front. Main forcing mechanism through the afternoon appears to be daytime heating. HRRR blossoms precip north of the front late this afternoon...but it diminishes quickly by the evening when heating is lost. Forecast soundings continue to show some limited instability...but feel that the HRRR...appears a bit over done. However...will include a low chc for a shower near the front...mainly far northern areas late this afternoon. Grids will be dry after 00z as heating will be lost and forecast soundings continue to reveal a dry column and time heights show subsidence. Back door cold front is expected to make slow and stead progress southwest tonight as the ridging aloft to our west builds across Indiana. THe lower level boundary may help to provide some clouds during the night as time heights suggest some lower level moisture available. Thus will trend toward a partly cloud sky overnight...with a blend on temps. && .SHORT TERM /Saturday through Monday/... Issued at 141 PM EDT Fri Sep 23 2016 Dry Weather is expected for much of the weekend as HIgh pressure northeast of Indiana and the previously Mentioned ridging aloft continue to dominate Indiana/s weather. Models suggesting cooler...northeast flow on Saturday and Sunday and this should provide slightly cooler temperatures...however it will still be above seasonal normals. Forecast soundings on both Saturday and Sunday Afternoon indicate convective temperatures that can be reached...however CAPE is very limited. Thus will just trend toward partly Cloudy skies both afternoons...again trending slightly warmer than a blend on Highs. Late Sunday night and Monday appear to be the better times for precip. NAM and GFS push the upper ridge east of Indiana by that time as a deep upper low pushes out of the Central Canada and into the Great lakes and Ohio valley. This feature looks to push as cold front across the state with ample dynamics and will include raise pops...particularly monday as these features pass. Forecast soundings show best saturation on Late Sunday night and on Monday. We should continue to be mindful that these features often progress more slowly due to the strong departing ridge ahead of the front. && .LONG TERM /Monday Night through Friday/... Issued at 159 PM EDT Fri Sep 23 2016 Models are more progressive in recent runs with large low pressure system moving through the Great Lakes early to mid week. The cold front is now progged to be through the area prior to the start of the Long Term period, with broad surface high pressure moving into the area and dominating through the remainder of the period. Thus will carry a dry forecast throughout the period. As is noted above, however, there remains uncertainty in the departure of this system. Temperatures throughout the period will be pleasant, and much more in line with climatological normals than recent days. && .AVIATION /Discussion for the 24/00Z TAF Issuance/... Issued at 700 PM EDT Fri Sep 23 2016 Confidence is good that VFR conditions will deteriorate to MVFR or worse overnight in fog and or stratus as a frontal boundary slides drops slowly south over central Indiana. The local foggy program slightly favors stratus over fog, while the GFS LAMP favors fog and the SREF is more in the middle. At any rate, post-frontal IFR conditions will become more likely at LAF after 10z. The other sites could see MVFR or worse, but confidence at those sites is lower. Winds will be calm or very light and variable tonight and becoming east and northeast 5 knots or less on Saturday. && .IND Watches/Warnings/Advisories...NONE. && $$ SYNOPSIS...PUMA NEAR TERM...PUMA SHORT TERM...PUMA LONG TERM...NIELD AVIATION...MK
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
408 PM CDT FRI SEP 23 2016 .SHORT TERM...(This evening through Saturday) Issued at 408 PM CDT Fri Sep 23 2016 Another day and it`s more of the same for this week with PWATs near 2 inches (exceeding climatological records for the end of September)and more rain falling from the skies. The band out there now is a waa band that`s going up on elevated instability gradient based in the h85 to h7 layer. Though radar may not look all that impressive, the high PWATs are once again resulting in efficient rainfall producers, with KMPX dual pol radar estimates showing about an inch of rain was being produced by the band. Only hi-res models that have had much of a handle on this are ones that are rapid update (i.e. the hrrr) and we like the idea of this band continuing northeast into northern MN and northwest Wisconsin this evening while also weakening in terms of rainfall intensity. The weakening is the result of the instability feeding these showers not following them off to the northeast. For the rest of tonight, it will be another night of low stratus as we remain north of the warm front. As for the warm front, it is quite impressive this afternoon. It just sneaks into SW MN where Luverne was 86 degrees at 3 pm. At the same time, Pipestone right on the front was 77, while by the time you got up to Marshall it was only 65. And to boot, 90s were not all that far away with Yankton, SD sitting at 91. This warm front will not start lifting north until Saturday morning and will make it about as far north as the upper MN River Valley before it starts getting swept up by a cold front that will be pushing through Saturday night. As we have seen today, this is a very warm warm sector and if we get any clearing in south central MN tomorrow, then highs near 90 will be possible. However, for most it will be another day of extensive cloud cover and little diurnal temperature range. For precip, as we saw this morning, there will be potential for drizzle development here north of the warm front overnight, but once the band currently over the area moves off to the northeast, no significant precip arrives until the cold front starts nudging into western MN late Saturday afternoon. There was a general slowing of how quickly these storms get here, so did slow down how quickly we bring back PoPs tomorrow afternoon. There will be plenty of low level shear to support a severe weather threat, but extensive cloud cover will greatly hamper atmospheric destabilization. In addition, capping will be weak tomorrow, so once we develop instability, the atmosphere will quickly consume it. Still the top analog for the NAM forecast on Saturday of October 8, 1997 had a good deal of wind reports with a line of storms that developed ahead of a cold front, so the severe risk tomorrow is not negligible. Of course the one thing we don`t need right now is more rain, but that`s what is coming. In addition, the NAM/GFS again show PWATs up around 2 inches ahead of the front, so it`s back to more efficient rainfall producers and heavy rainfall. Fortunately the progressive nature of the activity looks to limit the flood threat with a general model consensus on a fairly widespread 0.5" to 1" out of this front. However, the NAM shows some streaks where around 2" are possible and given the hydrologic conditions of much of the area, even modest amounts such as that could lead to excessive rainfall issues once again and the slight risk of excessive rainfall from the WPC is warranted. .LONG TERM...(Saturday night through Friday) Issued at 408 PM CDT Fri Sep 23 2016 A long line of showers and thunderstorms stretching from the Canadian border to the Mexican border will develop Saturday afternoon and track east along a cold front Saturday night. Good forcing along the front and very high pwat values near 2 inches should keep the band intact through the CWA. Raised pops further from previous forecasts to around 100 over eastern MN and over 80 just about everywhere else. The severe threat appears marginal with a nearly saturated atmosphere and poor lapse rates. Still, should expect some gusty winds with the band of heaviest storms with decent low level shear. Cannot rule out a weak QLCS tornado as well with good veering profiles in the lower levels in areas that can achieve better instability. The dry slot will push in immediately behind the front with some clearing skies Sunday morning. The upper low will then push east across the Upper Mississippi Valley bringing widespread stratus across the region and scattered showers for the northern halves of Minnesota and Wisconsin. Depending how long it takes the upper low to eject northeast, we could see some showers linger into Monday night. GFS and GEM are the slowest, with the ECMWF the quickest. Usually the slower solutions win out in these circumstances so maintained such PoPs north of I-94 through Monday night, but did reduce them Tuesday and Tuesday night. Mid to late week looks quite pleasant with surface ridging pushing east across the eastern two thirds of the nation. A mid level ridge will build across the central CONUS, very likely keeping dry weather in place for much of the week. Southeast to south flow will also bring warmer temperatures. && .AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon) Issued at 123 PM CDT Fri Sep 23 2016 Elevated instability pushing in is forcing a band of shra/tsra across MN. The HRRR has had a good handle on it, though has not been building it far enough southeast. This band of shra will lift through AXN/MSP/STC/RNH on its way to northern MN and NW WI. In its wake, we remain north of the surface warm front tonight, which means more widespread IFR stratus through tonight, with IFR/MVFR vis developing as well, though that will be closer to the warm front, so a bigger issue from west central through south central MN. We may see cigs lift some tomorrow afternoon ahead of the cold front, with the next chance for TSRA lingering just outside current TAF period. KMSP...band of shra with embedded tsra continues to build southeast as it moves to the northeast and at its current pace will be to MSP around 20Z. Has become obvious more than a vcsh was needed, so started shra with a vcts at 20z. Rain shouldn`t last for much more than an hour, but in it`s wake is extensive IFR and lower stratus, which is a sign of our future tonight. /OUTLOOK FOR KMSP/ Sun...MVFR/-SHRA/-TSRA early, bcmg VFR. Wind W 10g20 kts. Mon...Chc MVFR/-SHRA. Wind WNW 10g15 kts. Tue...Chc MVFR early then VFR. Wind NW 5-10 kts. && .MPX Watches/Warnings/Advisories... WI...None. MN...None. && $$ SHORT TERM...MPG LONG TERM...BORGHOFF AVIATION...MPG
Area Forecast Discussion
National Weather Service Pocatello ID
150 PM MDT FRI SEP 23 2016 .DISCUSSION...Early afternoon satellite and radar imagery was showing the upper low centered near Salt Lake City with diminishing radar returns across SE Idaho. Numerical models continue to show the low lifting NE into Wyoming late this afternoon and eventually into SW North Dakota by Saturday afternoon. The NAM and GFS guidance appear to be overdoing QPF totals over SE Idaho (especially this past morning) and thus are falling under a specter of doubt whereas the HRRR and UofAriz WRF (two high-def short range models) are showing something more akin to what has been observed through early afternoon with diminishing returns this past morning and scattered showers continuing across the ERN highlands this afternoon and a continuous area of light rain over the ERN Magic Valley in the NW quad of the exiting low. Am favoring the two high-def models at this point and have decreased the precip potential this evening while leaving elevated chances across the ERN highlands tonight due to the passing low while drier conditions slowly spread into the CNTRL mountains/ERN Magic Valley. With that in mind, I have dropped the Flash Flood Watch for the South-Central Highlands, Caribou Highlands, and Idaho Portion of the Northern Wasatch for the remainder of this afternoon and evening. Snow levels are also expected to remain near 8000 to 8500 MSL across the NRN Wasatch this evening greatly reducing the likely hood of seeing any significant snow accumulations across the mountains near Bear Lake and thus I will allow the special weather statement for that areas 1st snowfall to go by the wayside as well. A ridge of high pressure builds across the NW states Sunday through Tuesday resulting in dry conditions. We may see a cold start Sunday morning with possible freeze warnings in the Snake Plain but otherwise temperatures should warm under the ridge peaking above seasonal normals Tuesday/Wednesday. By Wednesday afternoon the models are now showing the potential for a weak sub-tropical disturbance to lift NE through the CNTRL Rockies as a PAC trough takes shape off the NW coast. The NW trough eventually edges inland sometime Thursday/Friday resulting in increasing SW winds across the region and a chance/slight chance mention of showers favoring the mountains. Huston && .AVIATION...One airdrome, KSUN, has already broken out permanently from the effects of the current low pressure lingering over the Great Basin and northern Rockies. The other four airports will soon follow suit. KIDA should be next as northerly flow sets up a downslope and drying influence on the airport. KBYI has to contend with an upslope condition in the same flow, so it will continue to receive heavy rain, but once the wind shifts to the west this evening, conditions will lift quickly. KPIH and KDIJ will be the last to have clearing conditions as the low departs to the east. The main forecast problem is what the wind will do today at KBYI. Using a local study, it is indicating near Wind Advisory criteria, so have lowered wind there to 20G30KT. The current set up is rather weak on cold air advection, and the 500mb and 700mb flow is weak. Messick && .FIRE WEATHER...It is a tale of two areas; south and east of the Snake River, precipitation amounts for the last two days are approaching 1.50 inches, while areas to the north and northwest have not been hit as hard by the rain. High pressure will move in behind the low that brought all this rain late tonight and into Sat. This will start a warming and drying trend that should last at least into Wed, and perhaps even to next Fri. This is a long time to dry, but temperatures will struggle to even reach 80 degrees F, which makes it difficult for humidity to reach the teens. The one location that may be able to get low humidity is the Salmon-Challis NF and nearby BLM land, where dewpoints will lower into the 20s with the dry northerly flow on Sat and Sun. Fortunately, humidity criterion are not alone in a critical fire weather pattern. Moderate wind is also a minimum requirement, and as usual underneath high pressure, that will be difficult to get anywhere except at very high elevation. Messick && .PIH Watches/Warnings/Advisories...None. && $$
Area Forecast Discussion
National Weather Service Pueblo CO
344 PM MDT FRI SEP 23 2016 .SHORT TERM...(This evening through Saturday) Issued at 301 PM MDT Fri Sep 23 2016 ...A variety of high impact weather to continue across southern CO... An intense upper low over NW UT/SW WY will continue to lift northeastward with trailing trof axis swinging across southern CO during the evening hours...a little behind earlier model projections. This will put the brunt of the energy crossing the eastern mountains between 00z and 03z with strong downward forcing coming in quickly behind. Dry line has been slow to sharpen up...though in last hour dew point at COS plummeted from 39 to 15 degrees F...so once winds shift out of the southwest to west...it shouldn`t be too long before rapid drying takes place. Winds have been gusting to 40-50 mph at times and this will continue through the evening and overall Red Flag Warning still looks on track. To the east of the dryline...high res models are developing a broken line of thunderstorms between 4 PM and 5 PM. Dew points in the lower 50s yield mixed layer CAPE values of 1000 J/kg in SPC meso analysis. Deep layer shears will be running around 30-40 kts...so potential for one or two severe thunderstorms across the eastern counties still looks possible. Storms will be moving rapidly north northeastward with HRRR showing most of the activity done by 06z. Given high based nature to thunderstorms...main threat still looks to be winds over 60 mph and hail to around 1 inch in diameter. As the upper low lifts northeastward should see activity tail off from west to east...though northern portions of the Continental Divide may continue to see off and on snow showers through the overnight hours. Cold front moves in overnight...and a widespread freeze still looks likely for the San Luis Valley. Have upgraded the freeze watch to a freeze warning. Temperatures will be cooler elsewhere...but winds should keep temperatures from dropping too close to the freezing mark. Saturday will be cooler behind the front...though secondary push of cooler air will approach the Palmer Divide during the afternoon. Just enough moisture will be present along the CONTDVD and northern portions of the southeast mountains for some isolated to scattered showers and thunderstorms to redevelop...but overall...any precipitation looks light at this point. -KT .LONG TERM...(Saturday night through Friday) Issued at 301 PM MDT Fri Sep 23 2016 ...Feeling more like Fall on Sunday... The global models have come into better agreement today. The strong upper low moving through W CO today will split this weekend, with most of the energy lifting off to the NE. The base of the trough will cut off over W NM, then slowly eject to the NE during the mid to latter portion of the coming week. Sat night...the main low will be well north of our area...over the Nrn High Plains, while the trough axis is moving through E CO and the base of the trough beginning to split and cut off over NM. This will be the coldest air mass of the extended, with H7 temps getting down to around zero degrees over Teller County by early Sun morning. So...there could be a few snow showers above 9000 feet early Sunday, and possibly some light localized accums...but significant or widespread snow appears unlikely, and the latest model trends are for less QPF over the area. Main impact from this system will be considerably cooler wx on Sunday, with high temps only in the 60s for the Plains and 40s for the mts. WIll clear out pretty quickly Sun morning-afternoon, leaving our area with building high pressure from the west, which will keep us dry through at least Tuesday. Temps will gradually increase during this time period. By early Wednesday, the cut-off low to our south will finally begin moving into SW CO. This system will be much weaker than the current upper low, and with the Southwesterly trajectory, will also be quite a bit warmer aloft. So, snow levels will likely stay pretty high for the last week in September, generally above 12000 feet. Showers will be on the increase, especially for the latter part of Wed into early Thu. Have left mention of TS in the grids for this period since there will be some modest instability with the upper low. But for the balance of the forecast period, climatology does not favor widespread TS, so left any precip as Showers for the rest of this period. Once the second upper low moves through from the SW, our area will likely stay in an unsettled pattern with shortwaves moving through the Central Rockies. Current forecast assumes southwest flow over the CWA, so temps will remain generally above average. Rose && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 301 PM MDT Fri Sep 23 2016 South winds 25-40 KTS will shift around from the west during the late afternoon and early evening and remain gusty through 03-04z before gradually diminishing. TAF sites will remain VFR...but CONTDVD region will see off and on IFR to LIFR conditions in SHRASN through the early evening. Isolated TSRA will be possible to the east of the KLHX this evening...with the potential for a strong to severe storm or two through the evening hours. Clearing will take place through the evening...though some IFR to MVFR stratus may persist along the CONTDVD through Saturday morning. Winds will be much lighter on Saturday with another cold front expected to drop through the plains late Sat afternoon and early Sunday evening. -KT && .PUB Watches/Warnings/Advisories... Red Flag Warning until 8 PM MDT this evening for COZ226>233. Freeze Warning from midnight tonight to 9 AM MDT Saturday for COZ069>071. && $$ SHORT TERM...KT LONG TERM...ROSE AVIATION...KT
Area Forecast Discussion
National Weather Service SAN ANGELO TX
349 PM CDT FRI SEP 23 2016 .SHORT TERM... (Tonight and Saturday) The primary heavy rainfall event starts to occur Saturday Night, so the long term part of the discussion will deal with those concerns. For tonight, visible satellite shows some agitated cu across much of West Central Texas, but the latest HRRR is showing only a few isolated showers and storms developing this evening. This pretty well covered in the current forecasts so left that part of it alone. Convection will likely develop tonight to the west across the South Plains and Permian Basin as lift ahead of the large upper level trough axis begins to move into West Texas. These storms should slide east and increase in coverage Saturday afternoon. Have increased rain chances across the northwest Big Country, mainly north of a Sweetwater to Throckmorton line for Saturday afternoon. Areas farther south will wait for Saturday Night and beyond for their best chances. As for temperatures, mild again tonight as low clouds develop across much of the area by morning. Increasing cloud cover during the day on Saturday will begin to cut into afternoon highs. Still, enough sunshine in the afternoon for upper 80s and lower 90s, the hottest day we will likely see for the next week. 07 .LONG TERM... (Saturday Night through next Friday) The main focus is with the likelihood of heavy rainfall and the threat for flooding this weekend into Monday. By Saturday evening, an upper low is forecast to be over the Montana/ North Dakota border, with an upper trough extending south across western New Mexico. The GFS and ECMWF are in better agreement with the development of a closed low over southwestern New Mexico Saturday night. This low is progged to drop slowly south-southwest into Mexico on Sunday, and then retrograde slowly Sunday night into northwestern Mexico by Monday evening. With the northern part of the aforementioned trough progged to move east across the northern Plains on Sunday, trailing portion of a cold front is progged to move south into our northern counties Sunday afternoon, and then to make slow progress south through the rest of our area Sunday night and early Monday morning. Abundant moisture will be in place with precipitable water values 1.5 to 2 inches across our area, with low-level moisture influx from the Gulf of Mexico, and mid-high level moisture incorporated into the system from the eastern Pacific. In the Saturday night to Monday time frame, several disturbances aloft are progged to rotate around the eastern periphery of the upper low and into the western half of Texas. With this setup, anticipate several rounds of showers and thunderstorms with increased coverage and heavy rainfall. In addition, the slow- moving frontal boundary will provide an additional focus for heavy rain. Rain chances will ramp up Saturday night and continue through Sunday night, with likely PoPs extending through Monday. From Saturday night through Monday, widespread rainfall totals of 2-4 inches will be likely, with locally higher amounts possible. While our area can take some rain initially, expect multiple rounds of convection to saturate the ground and lead to excessive runoff/ flooding. A flash flood threat will also exist. We are monitoring this developing wet weather situation closely, and a Flash Flood Watch may be issued if the next set of models continue to show this setup for our area. Temperatures will be much cooler at the beginning of the week, especially on Monday. Rain chances will be lower, but still present in parts of our area Tuesday and Wednesday. Later in the week, temperatures are expected to warm back into the lower to mid 80s for highs (Thursday and Friday), when an upper level ridge tries to build back into our area. 19 .PRELIMINARY POINT TEMPS/POPS... Abilene 71 88 69 77 / 20 50 70 80 San Angelo 73 92 71 78 / 10 40 70 80 Junction 73 91 72 82 / 20 30 60 70 Brownwood 71 89 71 80 / 20 40 50 80 Sweetwater 69 88 69 73 / 20 60 80 90 Ozona 72 89 70 78 / 10 40 70 80 && .SJT Watches/Warnings/Advisories... None. && $$