Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/30/18

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
507 PM AKST Thu Nov 29 2018 .ANALYSIS AND UPPER LEVELS... The upper level longwave pattern has a trough extending out of Russia over the Bering Strait and then curving southeastward to Southcentral Alaska and into the Gulf of Alaska. The 250 mb jet stream is running west-to-east just below the Aleutian Islands and then splits with the main push heading southward under a trough in the Pacific and then continuing eastward. The section that splits northeastward is bringing a jet streak over the Eastern Aleutians and Alaska Peninsula today which will amplify some as it heads over southwest mainland Alaska Friday afternoon and then weakens Saturday over Southcentral Alaska. This is a big source for the warmer air moving into the area, but the big push of warm air will remain south of Alaska. At the surface there is an elongated low in the Bering Sea with centers in the northwest Bering Sea. The front associated with this low is moving into Southwest Mainland Alaska and then curves over the Alaska Peninsula. A low is beginning to develop along this front southwest of the Alaska Peninsula which will rapidly deepen tonight as it moves northeastward. The impacts of this will be talked about later in the discussion. && .MODEL DISCUSSION... Models continue to show a similar synoptic pattern but change run-to-run on details such as how far northward the warm sector of air reaches Friday and Saturday. Overall, the NAM and GFS look to be giving good enough information to be used, but there are still some challenges especially in forecasting precipitation type Saturday. && .AVIATION... PANC...With some partial clearing after the snowfall from the past day, it looks increasingly likely that there will be stratus and/or fog that will produce reduced ceilings and/or visibilities tonight through tomorrow morning. The current state of the atmosphere tilts a little more toward the stratus and less fog, but reduced visibility is likely. && .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)... (Tonight through Saturday) An interesting weather day is in store for the region as we head into the Friday evening through Saturday morning timeframe. More on that in a minute. Earlier we hoisted a dense fog advisory for the Glenn Hwy from Chickaloon to near Glennallen, as area web cams showed visibilities to near zero at times. With a transient ridge building overhead, this will likely continue through early afternoon tomorrow. As a side note, the afternoon sounding from Anchorage showed multiple low-level inversions already developing, but this can be seen even better on the King Salmon sounding. Then the real fun part of the forecast begins Friday evening, with the fun being will the models lock onto a solution in terms of the finer details, such as how fast will surface temperatures warm and thickness levels increase. As has been the case for the past couple of days, the NAM appears to be too aggressive with the warm advection at 850 mb. Meanwhile, the Canadian Regional, ARW, and HRRR models are slower with the warming at this level, and more so at the surface. This then leads to concerns for a period of freezing rain developing, as 850 temps warm above zero while the surface temps remain below freezing. The latter of the three models all differ on how long of a period this potential is. So in short, look for patchy fog overnight and during your morning commute, then for snow to gradually change from snow, to freezing rain, to rain for portions of Southcentral in the Friday evening through Saturday morning timeframe, with all locations changing back to snow Saturday night. && .SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3/Thursday night through Sunday)... The first of two fronts is currently on the doorstep of the Southwest coast with snow beginning to spread inland over the YK Delta. Ahead of the front, southeasterly winds are increasing and are expected to peak overnight as the front pushes inland. Snowfall totals will be on the lighter side with this system due to the quick movement of the front; however, blowing snow will be a concern overnight from Dillingham to Bethel as the southerly wind gusts in combination with the falling snow will reduce visibilities to around one mile at times. Although warmer air is advecting in aloft, temperatures are expected to stay cold enough for precipitation north and east of Dillingham to fall primarily as snow. Enough warmer air is expected to move in for areas around Bristol Bay where a changeover to rain will take place by early tomorrow morning. A North Pacific low will then begin to track northward, lifting a warm front across the region beginning midday Friday. With the center of the low tracking to the west of the mainland and a strong southerly flow ahead of it, this system will advect much warmer air over the southwest mainland. Rain will continue along the AKPEN and around Bristol Bay with snow quickly transitioning to rain farther inland as the front lifts north and the moves into the eastern Bering. Snowfall amounts will once again be light and mainly confined to far interior location like Aniak and Sleetmute as well as into portions of the Kuskokwim Delta where the colder air will linger the longest. As the warmer air works north, there will also be a narrow band of mixed precipitation as snow transitions to rain. Most of it will be a rain/snow mix, though there is a chance for a brief period freezing rain north of Bethel toward Hooper Bay. By early morning Saturday, colder air will begin to wrap around the northward tracking low changing any lingering rain showers back to snow. This weather pattern then repeats itself for late Saturday into Sunday as yet another system moves toward the southwest mainland from the north Pacific with another snow to rain precipitation event. && .SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3/Thursday night through Sunday)... Behind this front, zonal flow will develop over the western Bering for the next couple of days as vertically stacked low east of Kamchatka remains stationary. Intermittent small craft winds and periods of rain/snow will develop within this zonal flow as shortwaves eject from the parent low and transit over the southern Bering. Conditions remain quite active over the eastern Aleutians and Bering, however, as the first of two North Pacific lows lift north into the eastern Bering. The first is a double- barrel low and slides into the eastern Bering tomorrow. As this system intensifies, widespread gales and areas of storm-force wind will develop from the eastern Aleutians north to Cape Newenham. The second low then lifts north Saturday with another round of widespread rain and gales for the eastern half of the Bering and Aleutians. && .LONG TERM FORECAST (Days 3 through 7)... The forecast period commences with a longwave trough across the Central Bering and portions of the North Pacific with a ridge axis over the Yukon Territory and the Gulf Of Alaska. Between these longwave features southwest flow aloft will dominate much of the mainland. There are numerous shortwaves embedded in the upper level trough. At the onset of the forecast period, the Canadian/GFS and ECMWF have a surface low near Dutch Harbor, another surface low west of St. Matthew Island and a dome of high pressure east of SE AK. Even at the onset of the forecast period the global models struggle with the placement of the surface low although they have these features. As the forecast period elapses, the model divergence becomes more amplified. Generally speaking, expecting a progressive and unsettled pattern for the Bering, the Aleutians and SW AK. However, due to the lack consistency, this forecast package reflects a blend of models. && .AFC WATCHES/WARNINGS/ADVISORIES... PUBLIC...None. MARINE...Storms 155 165 172. Gales 132 138 150 160 170 173-176 180 181 414. && $$ SYNOPSIS AND MODEL DISCUSSION...EZ SOUTHCENTRAL ALASKA...PD SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM LONG TERM...PS
Area Forecast Discussion
National Weather Service Bismarck ND
948 PM CST Thu Nov 29 2018 .UPDATE... Issued at 944 PM CST Thu Nov 29 2018 No changes to dense fog headlines with this update. Surface observations and area web cams still showing dense fog within the advisory and good visibilities outside of the advisory. All other weather elements mainly on track. UPDATE Issued at 727 PM CST Thu Nov 29 2018 Will add McLean County to the Dense Fog Adv with fog spreading slowly west across the county based on reports from the McLean County SO. UPDATE Issued at 640 PM CST Thu Nov 29 2018 Main update early this evening was to issue a dense fog advisory across much of my central and north. Area web cams, surface observations, and several real-time reports all indicate dense fog developing across much of my north and central counties. Updated the aerial coverage and magnitude of the fog using a blend of the HRRR & RAP. Sky cover was also tweaked based on latest sat imagery and high res guidance. && .SHORT TERM...(This evening through Friday) Issued at 318 PM CST Thu Nov 29 2018 Snow with the threat of freezing rain will affect the southwest half of the state Friday night through Saturday night. See the long term discussion below for these details. Redevelopment of fog tonight is the main focus of the short term period of the forecast. Currently, a surface warm front extended from a low over southwestern Saskatchewan...southeastward across the northeastern corner of Montana and the northwestern corner of North Watford City...near New Salem and east of Hettinger. The warmer, drier air behind the warm front scoured out the stratus clouds and fog earlier today as it moved east to its present location. While the warm front aloft continues to move eastward across the state, the surface front is forecast to stall or move much slower eastward tonight. The latest high res models indicate fog re-developing and the current stratus deck remaining and expanding even a tad westward...tonight. Whether the fog will become dense (visibilities less than 1/2 mile) is more of a matter of when/where rather than "if." Thus for now have mention of areas of fog tonight for all but the southwest, where the warmer air has already pushed in and where the models indicate it will maintain its position. Looking at lows in the 20s tonight across our area. On Friday, we may see the stratus exiting to our east by late morning, only to see stratus development/redevelopment from the south as attention turns to the developing storm system setting up over the central Plains. There is a chance of rain, snow, or freezing rain southwest and south central by late afternoon. See the long term portion for this scenario discussion. Looking for highs Friday ranging from the upper 20s in the Turtle Mountains to the upper 30s in the southwest. .LONG TERM...(Friday night through Thursday) Issued at 318 PM CST Thu Nov 29 2018 Chance of light snow and freezing rain Friday night through Saturday night highlights the long term portion of the forecast. An upper level low over California today (Thursday) will move east across the southern Rockies and emerge in the Southern Plains Friday afternoon, then intensify as it lifts northeastward into the Central Plains Saturday, reaching the Great Lakes by Sunday morning. This large storm system will bring widespread precipitation across much of the southwestern and central US. The bulk of the precipitation with this system should be to our west, south, and east as the system progresses through the weekend...but will affect mainly southwestern counties in North Dakota. The 12z runs of the models are developing a more pronounced inverted trough extending from the central Plains low northwestward into eastern Montana, clipping the southwestern portion of North Dakota. This will favor more precipitation farther into southwestern North Dakota than was forecast in the past couple of days. Forecast soundings indicate plenty of low and mid level moisture moving northward into the state, but also a warm layer aloft advecting in along and north of the inverted trough. Then drier air aloft pushes in from the northeast on Saturday with a continued saturated boundary layer. This scenario will result in chances of both light snow and freezing rain late Friday afternoon through Saturday night for all of southwestern North Dakota...and reaching at times into northwestern and south central parts of the state. Snowfall and freezing rain implications Friday night through Saturday night: The more likely scenario is for 1 to 4 inches of snow to fall along and southwest of a line from north of Beach to Dickinson to Fort Yates, with highest amounts near Bowman and Hettinger. Areas along and south/west of the Missouri River will also be under the threat for freezing rain mixing in at times with the snow. Mainly dry and cool for Sunday into next week. Canadian high pressure pushes south into North Dakota Sunday and Monday, then northwest flow aloft with a couple of fast-moving clipper systems keeps off and on low chances of light snow in the forecast. Highs in the upper 20s to lower 30s Saturday...then cooler with highs mainly in the teens and 20s and lows Highs mainly in the 30s Friday, then a gradual cooling trend through early next week, where high temperatures are forecast to be in the teens and 20s, with lows in the single digits and teens above zero. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 640 PM CST Thu Nov 29 2018 VFR expected at KDIK through the 00Z TAF period. IFR-VLIFR cigs/vis expected for KMOT/KJMS tonight with low stratus and periods of dense fog remaining widespread across much of northern and central ND. Some improvement later Friday morning expected. KISN will be on the edge of the stratus and may remain mainly VFR through the period. Though occasionally dips and vis and/or cigs will be possible overnight. KBIS remain in dense fog and VLIFR cigs. Some improvement overnight is suggested by models. KBIS will likely fluctuate overnight from VLIFR to MVFR conditions as high res models keep the western edge of the stratus right over the terminal. && .BIS WATCHES/WARNINGS/ADVISORIES... Dense Fog Advisory until 10 AM CST Friday for NDZ001>005-010>013- 021>023-025-035>037-046>048-050-051. && $$ UPDATE...NH SHORT TERM...JV LONG TERM...JV AVIATION...NH
Area Forecast Discussion
National Weather Service Des Moines IA
551 PM CST Thu Nov 29 2018 .SHORT TERM.../Tonight through Friday/ Issued at 337 PM CST Thu Nov 29 2018 The primary concern through the period will be precip trends into this evening, followed by fog overnight. An elongated short wave/PV anomaly extends NW-SE just south of the MO River Valley and will continue to push west through the early evening hours. Much of the forcing is kinematic 3km and above with neutral lift to even slight subsidence below. This has resulted in high ceilings and soundings struggling to get much movement toward saturation around 1km. Even so, light rain and/or freezing is in progress and should continue into the early evening hours. Some sleet may also mix in as the column begins to nudge toward wet bulb temperatures aloft. The stronger H7/H5 QG forcing should be into DVN`s area by 00z however so the precip intensity should diminish some by that time. This is also reflected in the HRRR and RAP simulated reflectivity which gradually fades over the next several hours. Thus have mentioned a broad brush light rain/freezing rain/sleet wintry mix into the early evening hours. After the precipitation ends, weak upstream surface ridging will settle into Iowa with winds becoming nearly calm. The 20z surface analysis also noted higher surface dewpoints upstream just west of the MO River and these are expected to ooze into Iowa along and behind the ridge. This will produce conditions favorable for widespread fog to develop to varied degrees. With temps below freezing, there may be some freezing fog/frost development if visibilities drop sufficiently. Any fog should dissipate Friday morning but some cloudiness may linger through the day ahead of the next system. .LONG TERM.../Friday night through Thursday/ Issued at 337 PM CST Thu Nov 29 2018 The weekend storm system remains the primary challenge through the forecast period. Upper level low pressure is now moving over California this afternoon. This system will transition to an open wave as it moves east into the intermountain west tonight before closing off again as it moves to the lee side of the Rockies on Monday. The system will then lift northeast into Kansas Friday night and into Iowa on Saturday. There are a plethora of forecast challenges with this system. Initially, convective parameters are favorable for thunder development Friday night into Saturday as the initial kinematic and theta-e forcing arrive. Initially there will be a warm layer in place as the precipitation arrives and full profile saturation occurs. This may lead to a period of freezing rain across portions of the area north of highway 30 before dynamic cooling occurs and switches the precipitation to snow. Surface temperatures and wet bulb temperatures at this time are still in flux as minor adjustments will have large impacts on forecast precipitation types and amounts. The cooler NAM12 and GFS FV3 solutions followed by a slightly warm GFS deterministic then a warmer ECMWF. Given developing northeast winds during this period with the sfc warm front well to the south, current blended temperature solutions are likely overdone with warmer MOS guidance influence. Given all of this, suspect a lean to cooler solutions is more correct. The other issue is timing of the arrival of the dry slot aloft and the loss of ice introduction. Blended solutions for ProbIce are problematic and too low at times trying to blend different temporal solutions and diluting results in addition to likely ice introduction from underdone convective elements. Initial snowfall will occur with profiles nearly isothermal through the 0C to -3C range to near 700 mb with strong forcing through this layer. This will promote efficient aggregate dendritic growth that will result in large sticky flakes which may occur over a 3-5 hr period over portions of the northwest. This is similar to past events that have caused power outages due to tree damage impacting powerlines. Will continue to heighten the awareness of this in the watch area. Gusty northeast winds over 30 mph across the north/northwest will further enhance these concerns. Blowing snow potential at least initially looks low considering the wet sticky snow early. Some accumulations as colder air arrives with snow more susceptible to blowing will occur later in the event. The upper level system will shear out over the state Saturday night with a fragment moving southeast and another segment to the northeast. This will keep precipitation continuing overall and with colder air gradually spilling further south. Precipitation forecast during this period is difficult as there will likely be more intense areas of precipitation near fragment pieces of forcing still passing across central Iowa. Overall, expect heavy snow to occur over the far northwest with a mix of freezing rain/sleet/snow/rain occurring north of highway 30. Enough icing and snow may occur from near Denison to Iowa Falls and to Waverly to expand the watch for impacts. Still can not discount a further expansion south if colder air is a bit farther south. Over the south, rain and or thunderstorms early then transitioning to drizzle during the day Saturday followed by a transition to wintry weather Saturday night and Sunday. Ice intro is lost again over the north by Sunday and could lead to more freezing drizzle. Generally quiet and cold following this system next week with little to no precipitation forecast through Wednesday night. && .AVIATION.../For the 00Z TAFS through 00Z Friday evening/ Issued at 550 PM CST Thu Nov 29 2018 Complicated package. Areas of light freezing precip and light rain through 06z with fog likely overnight. Hires models hit most sites hard with at least 1/2 to 2sm and some areas down to 1/4sm by 09z through 13-15z. Signal has been around for several days as to possible fog, but confidence in areal coverage not as great. Will continue to monitor and make adjustments for 06z package. Aft about 15-16z...visby improves but lower MVFR cigs may linger. /rev && .HYDROLOGY... Issued at 337 PM CST Thu Nov 29 2018 RFC QPF ensemble hydrographs show significant within-bank rises expected on many streams--especially smaller ones--across at least the southern half of the CWA in conjunction with the seasonally moderate to heavy rainfall from Friday night into Saturday. The only instance of flooding indicated is borderline minor flooding along the North Raccoon River near Perry. Flooding concerns are less than previous forecasts, however, due to the expected more southern track of the storm and the rather progressive nature of the heaviest rainfall. NOHRSC snow depth shows between 0.8 to 1.6 inches of liquid within the snow pack over southern Iowa. The deeper snowpack as analyzed by NOHRSC is across portions of Clarke, Union, Ringgold, Decatur, Monroe, and Mahaska counties and correlates well with COOP observed values of 7 inches at Osceola and Albia reported this morning. In these areas, the rain will add to the existing snow-water equivalent. Elsewhere, the snow pack may melt with the rain adding additional water to nearby streams. Even where there is no snow pack farther north over central portions of central Iowa, much of the rain is expected to runoff with frost in the ground. With the runoff, significant rises are expected on rivers and streams with isolated minor flooding possible. && .DMX WATCHES/WARNINGS/ADVISORIES... Winter Storm Watch from Friday evening through Sunday morning for IAZ004>007-015>017-023>028-033>037-044>046. && $$ SHORT TERM...Small LONG TERM...Donavon AVIATION...REV HYDROLOGY...Zogg
Area Forecast Discussion
National Weather Service Sioux Falls SD
540 PM CST Thu Nov 29 2018 .SHORT TERM...(This evening through Friday) Issued at 325 PM CST Thu Nov 29 2018 Weak short wave passing to the south leading to potential for very light precipitation along highway 20 in Northwest Iowa through early evening. Fortunately, temperatures have warmed above freezing there, so moisture will have minimal impact. Low lying stratus oozing south across the forecast area this evening. Could lead to some areas of fog. Both NAM and HRRR have fairly widespread fog across the area, so will need to keep an eye on this through the overnight hours. Any lingering fog will try to lift into stratus during the day on Friday, but low lying clouds should impact warming through much of the day. Have kept temps in the 30s for highs. .LONG TERM...(Friday night through Thursday) Issued at 325 PM CST Thu Nov 29 2018 Focus this forecast is the upcoming winter storm Friday night through the weekend. Models are in general agreement on the system, but there are still details that are fuzzy. One thing that has been consistent with this system is the amount of moisture that is available. With the gulf wide open ahead of this system, precipitable water values climb to nearly 3/4" in the upper Midwest, which exceeds the 90th percentile for this time of year. With the 12Z runs, still some discrepancy on the precise track of the system. GFS is offering the furthest north solution, and the Canadian is the furthest south. For this iteration, sided closer to the ECMWF and NAM. On the large scale, models suggest large broad scale lift developing within low level warm air advection lifting north into the area. Not a lot of frontogenetic forcing to latch onto with this system, suggesting a prolonged snow event. EPV* is weakly stable in the early part of this system, and becomes increasingly stable throughout the day on Saturday. Models suggest that jet dynamics increase the lifting potential over the forecast area throughout the day on Saturday, gradually decreasing Saturday night into Sunday. Have concentrated highest pops south of highway 34, where the isentropic lift resides throughout the day on Saturday. Precip type appears to be difficult with this system, especially through mid day Saturday as cold air starts to collapse south. The NAM indicates a warm nose of air feeding into northwest Iowa and continuing into southeast South Dakota Friday night into Saturday morning. This overlaps the increasing lift, potentially leading to an area of sleet/freezing rain on the northern edge of the developing precipitation. Have raised icing potential in an arc extending from near Spencer Iowa to Mitchell South Dakota, with around a tenth of an inch of ice possible. As the colder air shifts south on Saturday, expect precipitation to change over to snow. Moderate snow should continue well into the evening, possibly into Sunday before it gradually comes to an end. Winds will also be breezy on Saturday with 20-35 mph north-northeast winds through much of the event. Models still seem to be a bit uncertain on how quickly this system will shift to the east, but in general seem to hint that system will linger at least through Saturday night if not into Sunday. Have raised pops through mid day Sunday, and extended headlines through 00Z Monday with strong winds continuing through the day Sunday. In regards to headlines, have upgraded to a winter storm warning across south central South Dakota. Further to the north and east, uncertainty remains with precip types and amounts so have left the watch going. Models also suggest a sharp gradient on the north edge of this system, but where that sets up is unclear. If we do see near a tenth of an inch of ice along with the winds, am concerned about impacts to power system and trees in the area. Weather quiets down next week, but temperatures cool remaining well below freezing through the week. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 538 PM CST Thu Nov 29 2018 Hedged toward a pessimistic forecast through much of this TAF period, as low stratus likely to lower even further beneath strengthening inversion. This expected to result in IFR-LIFR visibility in fog in many areas by late evening through the overnight hours into Friday morning. Subtle improvement to MVFR conditions possible by midday Friday, but watch for deteriorating conditions again after the end of this TAF period. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...Winter Storm Warning from 6 PM Friday to 6 PM CST Sunday for SDZ050-063>065-068-069. Winter Storm Watch from Friday evening through Sunday afternoon for SDZ052>062-066-067-070-071. MN...Winter Storm Watch from Friday evening through Sunday afternoon for MNZ089-090-097-098. Winter Storm Watch from Saturday morning through Sunday morning for MNZ071-072-080-081. IA...Winter Storm Watch from Friday evening through Sunday afternoon for IAZ001>003-012>014-020>022-031-032. NE...Winter Storm Watch from Friday evening through Sunday afternoon for NEZ013-014. && $$ SHORT TERM...SG/BT LONG TERM...SG/BT AVIATION...JH
Area Forecast Discussion
National Weather Service Hastings NE
921 PM CST Thu Nov 29 2018 .UPDATE... Issued at 900 PM CST Thu Nov 29 2018 Rapidly falling temperatures and light southeasterly winds have allowed dense fog to develop in spots the past couple of hours. As this fog is becoming more widespread...opted to issue a dense fog advisory through 9 AM CST for much of south central Nebraska based on latest model guidance...but will keep an eye on things as it may need to be expanded further south and potentially into portions of north central Kansas later tonight. && .SHORT TERM...(This evening through Friday) Issued at 339 PM CST Thu Nov 29 2018 Aloft: RAP model analyses of the tropopause...12Z upr-air data and GOES-16 WV imagery showed zonal flow over the CONUS. A weak shortwave trof was crossing Neb/KS and was responsible for the clds and the -RA along and N of I-80. By far the feature of greatest interest was the low over Nrn CA. This low will weaken tonight- tomorrow as its remnants lifts into the Nrn Rckys. Meanwhile...the remaining trof will dig over the Desert SW tonight and become negatively tilted tomorrow as it swings into W TX. As all this occurs...the weak trof currently over Neb/KS will move E of the rgn with a shortwave ridge moving in tonight. Winds will back from WSW- SSW as the trof approaches tomorrow. Surface: The CWA was in a non-descript pres pattern...between a very wk low pres sys over the Nrn Plns...and the prvs cool front that moved thru which was stationary from CO-OK-AR. A couple lows were already along that front. Weak high pres will gradually evolve over the Midwest thru tomorrow as the Nrn Plns sys conts to move E. Meanwhile...cyclogenesis will ensue over the OK panhandle tomorrow. Model consensus has the low around 994 mb. This afternoon: -RA has been persistent over the Nrn 1/3 of the CWA. Mesonet sites show than up to 0.11" has fallen. Clds are rapidly moving E and the mdls are not handling this well. So made some manual changes to better reflect this. Tonight: Clearing will cont...but it will be temporary. Dwpts range from 37-42F and conds will be ideal for rapid cooling this eve...lgt winds and clearing skies. The fact that clds exist around 2K ft at at MCK/LBF/BBW also foreshadow fog potential. So expect fog to form...and it will probably form much earlier than usual. There is a lot of uncertainty on how much low stratus develops or if it evolves from the fog. Regardless...multi-model RH cross sections show mid-high clds will overspread the CWA from W-E after midnight. So it will become cldy one way or the other. Used warmer guidance for lows which raised them abv the prvs fcst (30-35F). Friday: Cldy/foggy. Low-lvl mstr could become deep enough for some drzl to develop after midday. Incrsg lift will result in the development of areas of light rain over KS that will lift N into the CWA during the afternoon. The thick cld cover will suppress the temp curve with highs only in the mid-upr 30s. .LONG TERM...(Friday night through Thursday) Issued at 339 PM CST Thu Nov 29 2018 Aloft: A low will form over KS within the neg tilt trof Fri night. Sat into Sat night the mdls are tightly-clustered indicating the low will lift into IA and slow or temporarily stall as the sys occludes. It will weaken Sun with its remnants moving into the GtLks. However...a shear zone will linger over Neb/KS as closed high forms over the Nrn Plns. This system will initiate amplification...carving out a longwave trof over the Wrn/Cntrl USA. While the 1st sys is moving thru...another low will move in from the Pac Fri night. It is fcst to dive thru the Desert SW and move thru KS Mon into Mon night. Meanwhile...split flow will develop over the E Pac with a high-over-low (-EPO) pattern. The Nrn stream will deliver an Arctic air mass that will result in very cold wx next wk. Surface: The deep low near EHA will move to near TUL by 12Z/Sat and then occlude as it lifts into SW IA by 00Z/Sun near 988 mb. The CWA will remain the cold sector of this low thru Sun with Canadian high pres beginning to build in. This high will expand S thru the Plns Mon-Tue. An Arctic cold front is fcst to drop into the Nrn Plns Tue. The tail end of this front should move thru here Wed AM. Precip: rain will cont to develop and blossom over the entire CWA Fri eve as deep ascent occurs and the commahead precip shield evolves. As colder air begins wrapping in after 06Z...the low- level temp profile will cool enough to allow a chgovr to snow W of Hwy 281. The rest of the rain will chg to snow Sat AM. The accumulating snow Sat will fall mostly along and N of Hwy 6. S of Hwy 6 temps should be marginal enough to remain rain/drzl or a rain/snow mix...espcly over Neb. There will probably be periods where no precip is falling. Any remaining rain will chg to snow Sat night...with periods of light snow lingering into Sun and possibly even Mon. The biggest uncertainty in this fcst is the potential for icing from frzg rain or more likely frzg drzl. This may be overplayed in the fcst...but the banded nature of the precip in the commahead will result in transient cld bands where the DGZ is saturated and snow falls. Where the DGZ becomes unsaturated though...frzg drzl could occur. Mdls: the 12Z GEM and 06Z/12Z GFS are tightly clustered with the 00Z/12Z EC 700 mb low over SE Neb/NE KS at 18Z/Sat. The 12Z/18Z NAM are outliers further W. So the NAM brings the dryslot into the CWA. That scenario would result in more of a frzg drzl scenario. We collaborated with WPC and adjacent offices on conf call at 1815Z. Warning/Advisory issued in conjunction with LBF/OAX. Snow: This is not set in stone...but as of now this is how we see it. (These totals are from late Fri night thru Sun eve). Please allow us wiggle room for adjustments. 1-3" from KS Hwy 36 up to Hwy 6 2-5" Hwy 6 to I-80 4-9" I-80 up to Ord/Greeley/Fullerton with the highest amts N Most of this accum will occur during the day Sat...but 1-3" of those amts will fall Sat night thru Sun. Keep in mind these amts are based on model averages. There will be narrow bands within the larger commahead precip shield that will result in more snow in some areas...and less in others. This is expected to be a long drawn-out event. Road crews should anticipate nuisance lighter snow continuing Sun into Sun night. Blowing/drifting will work against keeping roads clear. Winds diminish Sun night. Winds: not expected to be excessive. 15-25 mph with G30-35. That will result in blwg/drifting snow. Big travel delays expected espcly N of Hwy 6 and this includes I-80. Some county roads N of the Tri-Cities could become impassable. Prepare for cancellation of activities. Temps: Below normal Sat...then much below normal Sun-Thu as a 5-day stretch with highs below frzg ensues over S-cntrl Neb... where snow is laid down from this sys. && .AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Friday) Issued at 550 PM CST Thu Nov 29 2018 Deteriorating conditions are expected at both terminals this evening as temperatures rapidly drop...reaching dewpoints...and widespread fog develops. Was pretty pessimistic with fog overnight...with 1/2SM (or lower) expected at both sites. In addition to LIFR VSBYS...expect LIFR CIGS to develop as well...with those CIGS likely lingering into the daytime hours Friday as VSBYS gradually improve during the mid-morning hours. At the same time...expect an approaching disturbance to help generate some drizzle by midday...transitioning to more of a steady light rain towards the tail end...or just beyond...the scope of the current TAF period. && .GID WATCHES/WARNINGS/ADVISORIES... NE...Winter Weather Advisory from 6 PM Friday to 6 PM CST Sunday for NEZ060-064-072>077. Dense Fog Advisory until 9 AM CST Friday for NEZ039>041-046>049- 060>064-072>077. Winter Storm Warning from 6 PM Friday to 6 PM CST Sunday for NEZ039>041-046>049-061>063. KS...None. && $$ UPDATE...Rossi SHORT TERM...Kelley LONG TERM...Kelley AVIATION...Rossi
Area Forecast Discussion
National Weather Service Paducah KY
909 PM CST Thu Nov 29 2018 .UPDATE... Issued at 908 PM CST Thu Nov 29 2018 Several subtle, but important changes made to the evening and overnight forecast. Main adjustment this evening was to incorporate SPC probabilities for general thunderstorms overnight. Nearly all of the instability (as depicted through the RAP model initialization) is above the surface to 1 km layer, so any updrafts will be rooted above the boundary layer. Instability via the RAP ranges from 400-600 j/kg with little convective inhibition. KPAH is showing unidirectional southwest flow of 40-50 knots above 2kft msl, with some veering at the lowest levels. Moisture transport/advection continues to be good this evening, so do not anticipate any lack of a decent moisture gradient ahead of a weak mid-level trough. Although the SPC probabilities for general thunder are 30% or less across the southern and southeast parts of the WFO PAH CWA this evening, cannot rule out a lower probability of thunderstorms. Do no anticipate any strong or severe storms at all overnight. Some evidence of weak updrafts were evident in the cellular character of the developing showers this evening in the warm sector south of the frontal boundary poised on the northwest side of the WFO PAH forecast area. Most of the high resolution and medium range guidance continued to under estimate temperatures and dewpoints this evening by 1-2 degrees. The best initialization this evening actually came from the 12z Thursday Canadian model guidance and it was incorporated into the overnight temperature, dewpoint, and relative humidity calulations. Little, if any adjustments were made beyond 15z (9 am CST) on Friday to the current forecast. && .SHORT TERM...(Tonight through Saturday night) Issued at 303 PM CST Thu Nov 29 2018 Well the low overcast conditions have overspread the entire area today, and the modest south winds have forced a weak frontal boundary just north/northwest of our region. We have not had much if any drizzle or shower activity through the day, but KPAH is just now showing some drizzly weak echoes just southwest of the radar. 12Z NAM and GFS soundings indicate that the boundary layer will deepen enough this evening to create a shallow layer of instability beneath the mid-level inversion. This should result in scattered light shower activity throughout the area this evening. As a weak mid/upper-level disturbance moves eastward toward/through the area, the surface boundary will shift southeast through much of our region overnight, which will push the shower activity southeast to west Kentucky by 12Z Friday. Our likely PoPs may be a bit much for the shower activity alone, but drizzle will also be possible. Much of the area will be dry on Friday, depending on how far southeast the boundary makes it. There is some possibility that it will clear the entire region in the morning. We will maintain chance PoPs in the far southeast through the day to account for any lingering shower activity. The 12Z model consensus seems to have sped up the northward movement of the warm front Friday night, but the strongest surge of moisture and instability will still be from Arkansas into Missouri. Cannot disagree with the Marginal Risk for severe in our far southwest Friday night. Instability is still pretty meager which may make surface-based storms difficult to get. However, the wind field, especially in the lowest 3km is quite strong, so we will have to continue to monitor the situation for some stronger wind gusts and even tornadoes near the warm front. QPF has ticked up a bit, but is still in the 1-2" range Friday night through Saturday. The warm advection convection/precipitation is now expected to linger past 12Z over most of the region, and may linger into the afternoon over southwest Indiana and east of the Lakes. The severe threat will be minimal Saturday morning, as the convection may still be elevated. Once the dry slot arrives there may be enough low-level moisture and heating to break the cap along and ahead of the cold front through the afternoon. If storms can get going in the warm sector Saturday afternoon, a few may become severe with large hail, damaging winds and even tornadoes possible. This may be our best severe threat, but there are a lot of things that have to come together just right, so confidence is not great at this time. South winds will be quite strong on Saturday with or without storms. Some gusts over 30 mph will be possible, so will continue to mention in the HWO. Saturday night should be dry throughout the region. .LONG TERM...(Sunday through Thursday) Issued at 303 PM CST Thu Nov 29 2018 The weather pattern will return to the chilly pattern that has dominated most of November, characterized by anomalously low 500 mb heights across much of the US. Although the models agree on the large scale pattern, there are lots of inconsistencies regarding the shortwave details. These details will play a role in the timing of clouds and small precipitation chances early in the week. As for Sunday, there is good model agreement that residual troughing from Saturday`s system will extend southwest into the mid Missouri Valley. A dry southwest flow ahead of this trough will keep temps fairly mild, ranging from the mid 50s to mid 60s. The trough will swing southeast across our region Sunday night, starting a downward trend in temps. Model agreement fades quickly Monday through Tuesday due to a complicated split flow pattern at 500 mb. The past couple model cycles have increasingly suppressed the southern branch of the jet, so that our weather will be dominated by a series of shortwaves coming southeast in the northern branch. This trend will be reflected in somewhat colder forecast temps, with highs mainly in the 30s both Tuesday and Wednesday. Some patchy light rain or snow is still expected. Will keep small pops in the forecast for Monday and Monday night, but even on Tuesday some light snow cannot be ruled out, per the 12z ecmwf. Cold high pressure will cross our region mid-week. On Thursday, the high will move to our east, allowing temps to moderate slowly. A strong southern stream Pacific storm system will come onshore, preceded by 500 mb ridging over the southern Plains and lower Mississippi Valley Thursday. && .AVIATION... Issued at 531 PM CST Thu Nov 29 2018 For the 00z Friday WFO PAH TAF issuance, IFR ceilings and MVFR/IFR visibilities will be the rule as the moist boundary layer is lifted and produces light rain showers or drizzle through the evening. By late evening, especially for KCGI and KPAH, the warm frontal boundary will be further north enough to produce upper MVFR ceilings and visibilities. As the frontal boundary begins to sag back southward again between 06z-12z Friday, winds will veer around to the northwest, allowing ceilings to drop back into IFR category for the remainder of the forecast period. Conditions will definitely not be favorable for VFR rated aviation during this forecast period. && .PAH WATCHES/WARNINGS/ADVISORIES... IL...None. MO...None. IN...None. KY...None. && $$ UPDATE...Smith SHORT TERM...DRS LONG TERM...MY AVIATION...Smith
Area Forecast Discussion
National Weather Service Phoenix AZ
338 PM MST Thu Nov 29 2018 .UPDATE... Updated 18Z aviation discussion && .SYNOPSIS... A cold front is still expected to move across the region Thursday night into early Friday. The best chance for rainfall in the Phoenix metro area should occur Thursday evening into Thursday night. Expect a few lingering showers Friday mainly east of Phoenix. A much cooler and unsettled pattern will prevail this weekend and early next week, with temperatures Sunday into Monday nearly ten degrees below seasonal normals. && .DISCUSSION... The forecast remains on track with regards to the approaching Pacific low pressure system moving eastward across southern CA. At this hour, light showers are now beginning to break out across SE CA, but the dry subcloud layer is keeping most, or all rainfall from reaching the ground. Latest HRRR high-res model output pushing the sfc cold front and its associated line of showers into extreme western AZ by early evening, then across south-central AZ during the late evening/overnight hours. Latest consensus guidance is showing most areas getting at least some rain, but the rapid movement of the system keeping lower desert QPF`s down in the 0.05-0.20 inch range. Higher amounts can be expected over the higher terrain north and east of Phoenix, perhaps as high as 0.50 inch. The other impact from this system still is expected to be the winds, with localized gusts as high as 55 mph possible in extreme SW Imperial County and Joshua Tree NP. Some blowing dust is also possible across SE CA and SW AZ, but widespread low visibilities are not anticipated at this time. Given the fact that fcst sounding are showing few hundred joules of MLCAPE, slight chances for TS have also been added to the grids. Mountain snow will be limited to the highest peaks in Gila County. Showers should subside for most locations by Friday afternoon, although there will be enough lingering moisture to support some additional showers for Central Arizona, especially Gila County. For this weekend, another Pacific system passing well to our north will broaden the general troughing across the West. There will be some perturbations in the general flow aloft that could support additional showers. Precipitation chances peak again late Saturday and Sunday, primarily for locations from Phoenix eastward, but again, any accumulation looks skimpy. The most noticeable change to our weather from these two systems will prolonged cooler weather. The warmer desert locations will see highs in the low to mid 60`s beginning Friday complemented with much cooler overnight low temperatures. The coldest times are likely to be Monday and Tuesday mornings, particularly for Globe, where the low temperatures will drop at least a few degrees below freezing. Most other warmer locations will experience lows between 35 and 40 degrees at those times. Folks will see a gradual warmup in temperatures and quiet weather through the first part of the workweek. However, both the GFS and ECMWF deterministic models are becoming more bullish on another moist system similar to what we are seeing today moving through the area. If this holds, we could see additional rain/snow and prolonged cooler temperatures. && AVIATION... South-Central Arizona including KPHX, KIWA, and KSDL: A strong Pacific low and associated cold front will impact the Phoenix TAF sites beginning early this evening and continuing overnight with the primary impacts being gusty winds, showers, and decreasing ceilings. Light easterly winds will veer to the south around 20Z and southwest at 10 knots around 21-22Z, Winds will gradually increase ahead of the front which has slowed a bit and is expected to arrive between 03-06Z. Winds will be sustained at 15-20 knots with gusts in excess of 25 knots. Light to moderate rain showers are expected for a few hours around 06Z along and just behind the front, with winds decreasing below 15 knots around 09Z. An embedded thunderstorm may be possible with elevated instability aloft, but confidence is too low to include this in the TAF. Ceilings behind the front should also decrease below 5 kft, with MVFR ceilings possible after sunrise tomorrow. Southeast California/Southwest Arizona including KIPL and KBLH: A strong Pacific low and associated cold front will significantly impact southeast California this afternoon and evening with the primary impacts being gusty winds, blowing dust, and isolated showers. Southerly 10 knot winds will rapidly veer to the west- southwest with the frontal passage around 21Z, causing sustained winds above 20 knots and gusts in excess of 30 knots. Blowing dust will be possible this afternoon and early evening, so we have included a TEMPO group for reduced visibilities between 21-01Z at KBLH and 22-02Z at KIPL. Isolated light showers will be possible behind the front into the early overnight hours, with wind gusts decreasing below 25 knots by 09Z. If winds weaken and potentially decouple tomorrow morning, 20-30 knot wind shear in the lowest 2 kft will be possible, but confidence is too low to include this in the TAF at this time as winds currently look to remain elevated. Aviation Discussion not updated for amended TAFs. && .FIRE WEATHER... Saturday through Wednesday: Unsettled conditions will remain in place this weekend as a second weather system moves southeastward across the state. This will keep rain chances in the forecast for mainly high terrain areas each day with precipitation chances ending by early Monday. Breezy westerly winds are likely to be seen on Saturday before diminishing into Sunday. Fortunately, RH values will be above any concerning thresholds. Temperatures will be well below normals through the period with a bit of a warming trend late as higher pressure builds into the area from the west. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...Wind Advisory until 6 AM PST Friday for CAZ560-562. && $$ DISCUSSION...Percha/Deemer AVIATION...Hopper FIRE WEATHER...Kuhlman/CB
Area Forecast Discussion
National Weather Service Charleston WV
1018 PM EST Thu Nov 29 2018 .SYNOPSIS... Upper level weather disturbance and approaching warm front brings a return of rain chances tonight and Friday. Rain with another system this weekend. A couple cold fronts next week. && .NEAR TERM /THROUGH FRIDAY/... As of 1005 PM Thursday... Latest Radar trends indicating that rainfall is starting to develop and enter SW Virginia. However, 00Z NAM and the last several HRRR runs and other HI-RES guidance is showing that the rainfall will be more widespread over the southern and eastern CWA overnight into Friday morning as shortwave pushes through from west to east across southern West Virginia. Have lowered PoP to just a chance in the north and increased values across the Southern CWA. As of 545 PM Thursday... Lowered PoP over the next few hours as precip is taking a bit longer to come in than originally forecast. Did keep in the mention of a few sprinkles, as surface dew points remain in the 20s and likely the returns currently on Radar are not as intense at the surface than what the Radar is indicating due to this dry air in the low levels. Other than that, the forecast remains on track. Also should note that temperatures continue to rise with WAA, so when precip does eventually move into the area, it should fall as rain. As of 115 PM Thursday... Flurries/sprinkles have been observed at times today across the CWA due to isentropic lift. Otherwise, clouds are slowly increasing across the CWA, out ahead of an approaching warm front, and weak surface low, that will move into the area later tonight. Rain, will overspread the area late tonight, but should remain generally light, due to a lack of significant dynamics and moisture. In addition, temperatures over night should hold rather steady, and possibly rise a few degrees towards morning, and am expecting precipitation to be in the form of rain CWA wide late tonight. There could be a very brief period of freezing rain across the northern mountains, but overall, thinking if it does occur, coverage and duration will not be enough to cause issues. Surface low and front will drift east on Friday, with somewhat drier weather taking hold across the north. However, area will remain socked in with low clouds the entire day. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... As of 210 PM Thursday... The short term period is defined by a strong cyclone set to sail from the central Plains up through the Midwest into the Great Lakes region, leaving this area on the warm and wet side of things with continued warming through the period. Coupling between two 120+ kt jets, one accompanying the upstream side of a trough digging negatively into the Plains and another draped WNW to ESE across the Great Lakes/Northeast, offers robust upper level support for further development along a remnant frontal boundary positioned roughly along the Ohio River at the start of the period Friday night. Strong surface cyclogenesis accompanying the Plains jet/trough combined with strong divergence aloft in the northern Ohio Valley (due to the jet coupling) promotes strong southerly low- to mid-level flow across the South. This 50-70 kt southerly jet surges moisture into the region and overrides the surface warm front, producing widespread stratiform rain - well evident in isentropic analysis. At this time, the axis of greatest PoP, roughly mirroring the warm frontal band of rain, moves up from the SSW to the N starting early Saturday morning through the early afternoon. Best moisture convergence appears to be over the lower Ohio Valley up into northern IL/IN/OH, closer to the parent surface low, based on latest model guidance. But, PWAT still surges to 1.2-1.4" across our area, which is about as high as it has ever been based on ILN and RNK sounding climatology, during this time of year. So, while at this time the best chances for flooding rains appear just a bit outside of the area, the atmosphere will be juicy with plenty of potential for rain to become heavy at times, perhaps enough for some localized water issues, especially with saturated soils in place as has been noted in the previous discussion. Have remained with the same area in the HWO to highlight the flood threat, mainly along and West of the Ohio River. Currently forecasting roughly 0.5-1" widespread rainfall amounts saturday with highest amounts across SE Ohio and lowest near and East of the I79 corridor. Relying on hi-res models, a sharp decline in available moisture with the introduction of a dry slot aloft cuts heavy stratiform rain potential from W to E Saturday evening. Regarding severe weather potential, there is low probability for convection at all based on weak lapse rates and a warm nose in the mid-levels. Strong low- level flow and bulk shear as high at 90kts support long-lived, gusty showers at the least, though, particularly as a weak surface front passes through Saturday night. In spite of the weak overnight front, warm advection resumes Sunday with temperatures reaching the mid-60`s in the lowlands, with some guidance suggesting numbers near 70. But, lingering low-level clouds Sunday may stunt temperatures some, particularly in WV and near the WV mountains where clouds will hang on longest. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... As of 145 PM Thursday... The upper level pattern begins to change Monday as the eastern flank of a longwave trough inches closer into Central Appalachia Monday with several disturbances aloft drifting in behind the trough for the next few days. Winds shift out of a more northwesterly direction for the extent of the long-term, welcoming in colder air beginning Monday afternoon. Moisture associated with the upper level disturbances and their accompanying surface cold fronts will move in by the start of the period and hold steady through mid week. Discrepancies still remain amongst the models this far out in terms of the orientation of coverage, but colder air behind the front does suggest a change over to snow Monday evening in the mountains, as well as in the Lowlands by Tuesday evening. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/... As of 120 PM Thursday... A warm front pushes towards the region tonight with light rain expected. Conditions will also deteriorate through the night from MVFR to IFR as ceiling and visibility drop. Light rain and/or drizzle may persist through the day tomorrow with IFR conditions likely through the day. FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 00Z SATURDAY... FORECAST CONFIDENCE: High. ALTERNATE SCENARIOS: Precipitation timing and associated restrictions may vary from forecast. EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY OF WFO FORECAST TO AVAILABLE MODEL INFORMATION: H = HIGH: TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS. L = LOW: TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. DATE FRI 11/30/18 UTC 1HRLY 03 04 05 06 07 08 09 10 11 12 13 14 EST 1HRLY 22 23 00 01 02 03 04 05 06 07 08 09 CRW CONSISTENCY H H H H H H H H H H L L HTS CONSISTENCY H H H H L H H M L H M M BKW CONSISTENCY H H H H H H H H H H M H EKN CONSISTENCY M H H H H H H H H M M H PKB CONSISTENCY H H H H H H M M M H H M CKB CONSISTENCY M H H H H H H H L H M M AFTER 00Z SATURDAY... IFR possible in rain through the upcoming weekend. && .RLX WATCHES/WARNINGS/ADVISORIES... WV...None. OH...None. KY...None. VA...None. && $$ SYNOPSIS...MZ/SL/MC/MEK NEAR TERM...MPK/SL SHORT TERM...MC LONG TERM...MEK AVIATION...MPK