Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/23/17

Area Forecast Discussion
National Weather Service Bismarck ND
959 PM CDT Sat Apr 22 2017 .UPDATE... Issued at 953 PM CDT Sat Apr 22 2017 No big changes with the late evening update. Did the usual populating latest sensible weather elements and utilized radar/satellite to update weather/pops/sky cover. The latest couple iterations of the RAP and HRRR have shifted slightly farther south with a band of heavier snow late tonight into Sunday morning. The latest NAM is still farther north. Did blend a time lagged version of the HRRR/RAP to the previous forecast to shift the band of snow a little farther south, without a complete displacement. This did shift heavier accumulations (still under a couple inches) a little farther south into northern portions of Mclean, Sheridan, Wells and Foster counties. UPDATE Issued at 659 PM CDT Sat Apr 22 2017 Cold front has moved through all but far southern ND as of 6 pm this evening. Still some shower activity along and just behind the front over south central ND. Kept a mention of thunder here for another couple hours. In the north stratiform precipitation is currently falling as rain but temperatures around the Turtle mountains were already in the mid to upper 30s so they may switch over to snow this evening. Overall, very few changes from the going forecast. Updated products will be sent shortly. && .SHORT TERM...(This evening through Sunday) Issued at 333 PM CDT Sat Apr 22 2017 For the near term, now through sunset, cold front located from Beach to Bismarck to just north of Jamestown. Temperatures have warmed into the upper 60s to 70F in south central along and just ahead of the cold front. Compare this to 34F at Rolla. The cold front will continue a slow progress to the southern border by 03z Sunday. SREF 3hr calibrated thunderstorm probabilities increased to 10 percent south central ND through 00z Sunday. Given the steep low level lapse rates around 9c/km, most unstable cape around 250 j/kg and weak shear, have continued to mention isolated thunderstorms along and south of Interstate 94 through 00z. Latest radar shows isolated showers working into western Morton county and into Grant county, moving east with time. For tonight, low level frontogenesis increases across portions of north central ND. Expecting a moderate band of snow to develop between 03z-06z, and continue through the night. What appears will keep this event from reaching advisory level snowfall accumulations is the fact that the strongest synoptic scale forcing is displaced from the maximum frontogensis region. In addition, mid level lapse rates are marginal, around 6 to 6.5C/km. After collaborating with WPC and Grand Forks weather office, we have decided the best course of action is a Special Weather Statement for sub advisory snowfall. Expect snowfall accumulations of between 1 and 3 inches from Minot southeast to Harvey and Carrington; essentially between the Highway 2 and 52 corridor tonight through Sunday morning. Morning snow across north central ND, otherwise mostly cloudy and cooler Sunday with highs around 40F north to the mid 50s far south. .LONG TERM...(Sunday night through Saturday) Issued at 333 PM CDT Sat Apr 22 2017 Another round of precipitation still slated for Sunday night and Monday with a northern and southern stream shortwave shifting through western/central ND. Another inch of snowfall expected for most of the north central, along with a wintry mix into central ND Sunday night. Precipitation will change back to rain showers during the day Monday. Thereafter, generally dry but cool weather prevails Tuesday through Thursday. Highs in the 40s Tuesday and Wednesday, then 50s Thursday through Saturday. Chances for precipitation return Friday. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 953 PM CDT Sat Apr 22 2017 MVFR ceilings will drop south through the forecast area tonight behind a cold front. Expect widespread MVFR and occasional IFR ceilings Late this evening through the day Sunday. IFR ceilings most likely late tonight through mid morning Sunday. Occasional MVFR vsbys in rain and snow, most likely from KMOT to KJMS late this evening through early Sunday morning. A moderate northeast flow is expected through the forecast period. && .BIS WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...TWH SHORT TERM...KS LONG TERM...KS AVIATION...twh
Previous LONG TERM Forecast Discussion /Sunday Night through
The storm system affecting the short term period will carry over into the beginning of the long term. Parent closed mid level low will be located in the vicinity of the AL/TN border...with associated sfc low and cold front located across E/SE Georgia. Rain and thunderstorms will be ongoing along/near the cold front. Enough instability and shear looks to still be in place to support a chance for a few strong-severe updrafts...most so across southern CWA counties. The cold front should push east of the area overnight Sunday bringing an end to any/all severe chances. The closed mid level will sink slowly south across Georgia overnight Sunday into Monday. Left exit region of a weak upper level jet on the back side of this low...along with cooling mid level temps will be enough to support the development of scattered showers during this time period. Although mid level temps will cool...think post- frontal environment will be too stable overall to support any no thunder was put in the forecast overnight Sunday through Monday in association with the wrap-around moisture/dynamics. This stubborn low...along with all of its scattered shower activity should dissipate late Monday evening into the overnight hours. A very weak mid level ridge along with weak high pressure at the surface will keep conditions dry and rather pleasant Tuesday and Wednesday. By Thursday...H5 ridge and sfc high begin to slide offshore and the next frontal system will approach from the west. With dynamics displaced well north along with the lack of sufficient moisture return...think most frontal precip will fizzle upon approach. Have placed slight chance of thunder across northern tier for now. This front will lift as a warm front into the TN Valley on Friday as a sfc cyclone develops across the Southern Plains and ejects into the Midwest. Rather unclear at this point how this system will progress towards the local area...but a return to a moist southerly airmass looks likely at this point. Have opted to keep the remainder of the long-term fairly dry for now until a solution becomes more clear. Temps will be very pleasant to start the long-term...particularly Monday with highs in the 70s /60s mountains/ and lows in the low 50s. Gradual warming trend then expected...with highs mid-upper 80s by late in the week. Kovacik AVIATION... 00Z Update... Two waves of shra/tsra will move across the forecast through 00Z MON. The first wave will move across west and north GA this evening and early tonight. The next wave, associated with the cold front, will move across the region late tonight and Sunday. Both waves will bring the risk of thunder with the best chance on Sunday. CIGS will remain vfr this evening, becoming MVFR/IFR late tonight and continue MVFR through the day Sunday. Winds will be southwest less than 10 kts tonight, becoming west to northwest by Sunday afternoon, although AHN will see winds becoming northeast Sunday afternoon. //ATL Confidence...00Z Update... Medium on timing of shra/tsra. High on remaining elements. 17 && .PRELIMINARY POINT TEMPS/POPS... Athens 62 70 53 69 / 50 60 60 30 Atlanta 64 69 54 70 / 70 80 40 30 Blairsville 57 63 50 68 / 90 90 50 30 Cartersville 62 67 53 72 / 90 80 40 30 Columbus 64 74 54 74 / 40 60 20 20 Gainesville 60 65 52 69 / 80 80 50 30 Macon 61 78 55 72 / 10 60 40 30 Rome 61 67 52 73 / 90 80 30 20 Peachtree City 62 72 53 71 / 60 70 30 30 Vidalia 64 85 62 75 / 5 40 50 30 && .FFC WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...17 LONG TERM....RW AVIATION...17
Area Forecast Discussion
National Weather Service Green Bay WI
1012 PM CDT Sat Apr 22 2017 Updated aviation portion for 06Z TAF issuance .SHORT TERM...Tonight and Sunday Issued at 255 PM CDT Sat Apr 22 2017 The latest rap analysis and satellite/radar imagery show a high pressure ridge axis extending eastward across southern Minnesota and central Wisconsin early this afternoon. To the north, a cold front is dropping south over northern Minnesota. Widespread low clouds exist behind the front, with scattered rain showers and a few snow showers as well. As the front drops southward tonight into Sunday, cloud trends and precip chances are the main forecast concerns. Tonight...Mostly clear conditions will continue through the evening thanks to the linger effects of the high pressure ridge axis. But the cold front will make inroads into northern Wisconsin late tonight. Should see clouds increase there after midnight, with a few showers possible towards sunrise over Vilas county. Low temps will range from the mid 30s north to low 40s south. Sunday...The front will continue to move south into southern Wisconsin by late in the afternoon. Winds will shift to the northeast behind the front and bring in scattered to broken cloud cover generally north of highway 29. With the wind shift, temperatures are expected to fall over northeast Wisconsin during the afternoon. Will have a wide range of high temperatures, with clouds and a few showers keeping readings in the middle 40s over the north, while locations in Wood county may climb into the upper 60s before the wind shift occurs late in the day. .LONG TERM...Sunday Night Through Saturday Issued at 255 PM CDT Sat Apr 22 2017 Southwest upper flow will provide several chances for significant precipitation through the end of next week. Jet energy lifting northeast from the southern Plains should produce an inverted trough Monday night with a couple waves of low pressure moving northeast along a slow moving cold front. The first should bring rains and perhaps some snow in the far north Tuesday afternoon or evening through early Wednesday. The medium range models have different ideas of the track the next wave of low pressure takes. The ECMWF is furthest west and would bring another round of precipitation to the area Wednesday night and part of Thursday, while the GFS is much further east. A classic synoptic scale weather system is forecast next Sunday that could bring rain and perhaps snow to the region. Temperatures will be near normal Monday, above normal Tuesday and near or below normal normal for the rest of the week. && .AVIATION...for 06Z TAF Issuance Issued at 1004 PM CDT Sat Apr 22 2017 A Canadian cold front will drop into northern Wisconsin overnight and early Sunday, bringing MVFR and local IFR ceilings to parts of north central and far northeast WI. Scattered showers are also anticipated across the north toward daybreak, and lingering into Sunday. The front will continue to shift south on Sunday, and accelerate as it moves down Lake Michigan. Although clouds will also increase farther south, flight conditions should remain VFR in most spots, and little or no rain is expected. Surface winds will turn northeast to east in the wake of the frontal passage. West winds will increase to around 30 knots just off the surface overnight, but conditions are a little too borderline to add LLWS to the TAFs. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM.....MPC LONG TERM......RDM AVIATION.......Kieckbusch
Area Forecast Discussion
National Weather Service Jacksonville FL
923 PM EDT Sat Apr 22 2017 .UPDATE...Atlantic sea breeze moved well inland and now is through the middle of the CWA from central Marion county northward to the West Mims Wildfire to perhaps around Waycross and Alma. This shows up well in the latest MSAS analysis and HRRR guidance. Very little forcing aloft and instability is very little despite max temps that rose to mid and upper 80s inland. Model guidance has indicated for a few runs now that some weak convection might develop overnight over the srn zones as moisture increase a bit...but less confidence recently based on HRRR not being consistent and current radar trends. see some little development in satellite loops and perhaps some radar evidence of an isold shower or two possible late this evening and overnight over Marion and Putnam counties. Will maintain in fcst. A few showers or a thunderstorm possible over marine zones late tonight as well. Updated min temps to up them slightly and spread some patchy fog a bit further south for inland areas...though fog potential overall is low. Smoke from the large West Mims wildfire will begin to shift north then to the northeast after midnight, and is likely to impact areas across Charlton, Brantley, and Wayne counties. Towards daybreak, HYSPLIT output suggests Camden and Glynn counties may be impacted by smoke, possibly all the way to the coast. && .AVIATION... VFR conditions will continue to prevail. Winds will increase again out of the southeast behind the Atlantic seabreeze Sunday afternoon. Isolated thunderstorms may develop on the seabreeze along the I-95 corridor by late Sunday afternoon and then push back towards the coast. For now, we have added VCSH to account for this due to low probabilities at any given TAF site. && .MARINE...Main change was to put up SCEC headline for the next few hours based on short range guidance and SAUF1. Winds will turn to the south-southwest and drop off slightly toward early morning hours. && .PRELIMINARY POINT TEMPS/POPS... AMG 63 88 60 76 / 0 40 50 20 SSI 68 82 66 76 / 10 40 40 20 JAX 64 86 64 79 / 10 40 20 20 SGJ 67 83 65 78 / 10 60 20 20 GNV 62 86 61 79 / 10 20 20 10 OCF 64 86 64 79 / 20 40 20 10 && .JAX WATCHES/WARNINGS/ADVISORIES... FL...None. GA...None. AM...None. && $$ Shashy/Shuler/Walker
Area Forecast Discussion
National Weather Service Key West FL
1002 PM EDT Sat Apr 22 2017 .DISCUSSION... A large area of rain and showers continues to lift northward, remaining over the bulk of the Keys service area late this evening. There have been a few steady pockets of heavier showers and thunderstorms, but these have favored the Atlantic waters south of the Lower and Middle Keys thus far. Winds have remained from the east/southeast, and have fluctuated slightly in speed through the course of the evening. Most recently, they are on the upswing, remaining fresh. The late evening local sounding shows the veered profile remains in tact, but the depth of the fresher winds has decreased to the lowest layers. The local airmass is moist, with the precipitable water tally setting another daily record...2.10 inches. Quite moist for April. There is enough instability to sustain at least a few thunderstorms overnight. A mid level trough will steadily work eastward across the local area overnight. Beneath that, a relatively deep area of low pressure will lift northeastward across the local area. Based on the radar loop over the past several hours, in conjunction with the pattern in place, will hold on to the categorical probability of measurable precipitation overnight. The only reason for a late evening zone change would be to adjust the advertised winds upward through the overnight period. See reasoning in the marine section below. && .MARINE... The upcoming late evening coastal waters forecast will keep the small craft advisory for the offshore Gulf waters and all near and offshore Atlantic waters through the remainder of the first period. Although winds have fluctuated slightly over the past several hours, the most recent upward trend, along with the latest HRRR local solution point toward higher winds as the lower level cyclonic circulation approaches through the overnight period. However, directional shifting more toward the south should hold off closer to the daytime hours of Sunday. Admittedly, wind speeds may actually be borderline for several hours as far as the advisory is concerned, but with this unusual pattern, would prefer to error on the high side. Expect widespread rain showers with a few thunderstorms over the bulk of our marine service area overnight. && .AVIATION... Periods of MVFR CIGS/VIS, along with widespread showers will continue overnight with shower coverage gradually diminishing from west to east early Sunday morning. Easterly winds will gust to near 20 knots before decreasing to near 10 knots after 23/09z, while gradually veering and becoming southerly by daylight. Prevailing VFR will likely return after 23/15z. The thunderstorm risk seems minimal overnight, but certainly not out of the realm of possibility, and amendments to the terminal forecast will be issued if necessary. && .CLIMATE... On this date in Florida Keys History, in 1937, a high temperature of 88 degrees was recorded in Key West. This set the record for highest temperature measured for April 23rd for the city, a record which still stands 80 years later. Temperature records in Key West date back to 1872. && .KEY WATCHES/WARNINGS/ADVISORIES... FL...None. GM...Small Craft Advisory GMZ033-034-042>044-052>055-072>075. && $$ Public/Marine/Fire...04 Aviation/Nowcasts....MCLOVIN Data Collection......Fling Visit us on the web at Follow us on Facebook and Twitter at:
Area Forecast Discussion
National Weather Service Marquette MI
746 PM EDT Sat Apr 22 2017 .SHORT TERM...(This evening through Sunday) Issued at 324 PM EDT SAT APR 22 2017 12Z raobs/latest wv imagery and RAP analysis show a split flow dominating the wx pattern over NAmerica. Upr MI is on the srn flank of a nrn branch flat upr trof centered near Hudson Bay. A shrtwv embedded in this flow is tracking acrs far nrn Ontario, with attendant sfc cold fnt stretching fm sfc lo pres aprchg srn James Bay into nrn MN. Due to the warmth/dryness of the airmass ahead of this bndry per local 12Z raobs that has supported max temps into the 60s/rh falling as lo as about 20 pct over the cwa, there is an absence of pcpn and even much cld cover ahead of the slowly aprchg cold fnt. But on the cold side, there is a solid ovc and some light ra that changes to sn under a band of h7 fgen and with an influx of much colder air ahead of 12Z h85 temps as lo as -15C at The Pas Manitoba. Tngt...Lingering dry air associated with sfc hi pres retreating slowly to the se wl bring dry wx early in the evng, but then incoming cold fnt associated with the disturbance in the nrn branch tracking thru Ontario wl reach the Keweenaw by 03Z and then the far scentral arnd 12Z Sun. The band of pcpn under axis of h7 fgen on the cold side of the fnt wl arrive over the far nw cwa toward midngt and influence mainly the nrn tier with an upslope nly flow in the wake of the fropa. Although the pcpn, which wl start as ra but then mix with sn as colder air follows, wl be relatively light with an absence of sgnft mstr inflow and passage of sharper dynamic forcing to the n closer to the shrtwv track, there could be some wet sn accum over the hier terrain of nw Upr MI as min temps dip to 32. Sun...Hi pres bldg into nw Ontario under larger scale subsidence following the exiting shrtwv is fcst to extend a sfc rdg axis into the Upr Lks. Although the arrival of this rdg axis/some drier llvl air and acyc flow as well as weakening fgen wl tend to diminish any pcpn over mainly the nrn tier persisting in the mrng, a good deal of mid lvl mstr/cld cover wl linger near an h85-7 fntl bndry that remains near the area to the n of the sfc fnt that wl stall in WI. The best chc for some partial clrg in the aftn wl be over the ne cwa, which wl be more influenced by deeper drying. Did retain some lo chc pops thru the aftn over the w, where the drying wl be less emphatic. H85 temps falling as lo as arnd -6C over the Keweenaw and llvl nly flow off Lk Sup wl cause much cooler wx for the cwa, with hi temps holding in the 30s near Lk Sup. .LONG TERM...(Sunday night through Saturday) Issued at 333 PM EDT SAT APR 22 2017 With an active patterned expected through next week, we will see a roller coaster of temperatures with periodic chances for precipitation, including the potential for some snow. Sunday night through Monday morning, as upper-level energy lifts northeast of the area and flow becomes zonal across the region, the cold front that pushed south across the area on Sunday will stall out across central Wisconsin and lower Michigan. Upstream of the region, another system is progged to develop in the lee of the Rockies and lift northeast across the central Plains by Monday morning. Ahead of this system, warm air advection will begin to lift back north across the area. This elevated frontal zone will bring precipitation chances back to the area, especially across the west and north central. With the stalled out surface boundary expected to be south of the area, we will be on the cooler side of the boundary. Therefore, the combination of overrunning warm air and a pocket of colder air at low levels may promote the potential for a wintry mix of precipitation, including freezing rain, sleet, and snow. However, the dominant precipitation type will be highly dependent on the depth of the cold air at low levels and surface temperatures. During the day on Monday, the stalled front across central Wisconsin and lower Michigan will lift back north and allow for warmer air to overspread Upper Michigan, as the above mentioned low pressure system lifts northeast across the Upper Mississippi Valley. As temperatures warm, any lingering precipitation will transition over to light rain/drizzle. There should be a break in precipitation during the afternoon and evening hours on Monday as we break out into the warm sector. As this surface low lifts north precipitation chances will return Monday night and Tuesday as shortwave energy lifts across the area. This surface low is expected to weaken as it traverses the region, leaving behind a slow moving frontal boundary across the region, and extending down into the southern Plains, as mid-level flow becomes parallel to this boundary. Uncertainty does exists among the medium range models as to how far east the precipitation will get during the day on Tuesday, as the ECMWF is a bit more progressive with the eastward movement of the frontal boundary. At the same time, low pressure is expected to develop along the tail-end of the slow moving frontal boundary down across the southern Plains as a deep, longwave trough digs across the rockies and ejects out across the Plains. This developing system will lift northeast towards the region Tuesday night through Wednesday. This will allow precipitation chances to increase across Upper Michigan, especially Wednesday morning and through at least the rest of the day. While there is uncertainty among the models and ensembles in regards to the track and strength of the system, forecast soundings from the GFS/ECMWF do advertise thermal profiles becoming cold enough to support snow, at least across the western portions of Upper Michigan on Wednesday. Further to the east, medium range models showing temperatures aloft remaining just warm enough for precipitation to remain all liquid, but a transition over to snow sometime Wednesday night into Thursday looks possible as cold air advection increased on the back side of the exiting low pressure system. As mentioned above, there is quite a bit of uncertainty with this system and the details will likely change over the next few days, but this time period is something to monitor. The end of the week and beginning of the weekend look near normal temperature wise with high pressure dropping down from Canada. Precipitation chances look low at this time, with the deterministic models keeping precipitation well south of the area. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 746 PM EDT SAT APR 22 2017 A cold front will drop s across the area tonight, passing KCMX this evening and KIWD/KSAW overnight. Low clouds/IFR and even LIFR cigs along with some -ra changing to -sn will impact the terminals following the fropa and into Sun morning before the arrival of somewhat drier near sfc air allows for an improvement late morning/aftn. KCMX/KSAW will improve to VFR with stronger drying, while KIWD will improve to MVFR. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 333 PM EDT SAT APR 22 2017 WSW winds ahead of an approaching cold front as hi as 20-25 kts in the area between Isle Royale and the Keweenaw will shift to the N up to 20-25 kts tonight behind a cold front that will sweep across Lake Superior. These steady N winds will diminish and tend to veer to the ENE as a hi pres ridge builds over Lake Superior. Monday winds will become easterly and increase to around 15 to 25 knots. Throughout the day on Monday, winds will further increase to around 20 to 30 knots across much of the lake as an area of low pressure lifts out of the central Plains. Monday night into Tuesday, winds will veer to the southeast at 20 to 30 knots. Depending on the track of low pressure, a few gale force gusts may be possible. During the day on Tuesday as low pressure lifts across the area, winds of 15 to 25 knots are expected with south-southeast winds veering northwest. Overnight Tuesday into Wednesday, winds will further veer northeasterly and increase to 20 to 30 knots. Expect these winds to continue Wednesday and the first half of Thursday as another system develops in the Plains and lifts across the region. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...KC LONG TERM...Ritzman AVIATION...Rolfson MARINE...KC/Ritzman
Area Forecast Discussion
National Weather Service Paducah KY
725 PM CDT Sat Apr 22 2017 .UPDATE... Issued at 725 PM CDT Sat Apr 22 2017 Updated aviation discussion. && UPDATE... Issued at 453 PM CDT Sat Apr 22 2017 Dynamics, moisture, and forcing associated with the convection over the Tennessee Valley have decoupled somewhat, leaving the mean trough axis over Southern Missouri, Southern Illinois and Indiana separated from the mean flow. Until the jet dynamics/vorticity rotate around the sheared out low and deepen the it as the jet moves along the eastern side of the trough, will need to reduce PoPs and cloud cover on the northern end of the WFO PAH forecast area. Satellite trends still showing some lift along the southeastern section of the WFO PAH forecast area, so anticipate some isolated to scattered shower activity will regenerate as the low attempts to reform toward Southeast Missouri. Anticipate most of the lift will be confined to the south and east of the low through the overnight hours, so kept the mention of shower activty limited to that quadrant. The ESRL HRRR and the Canadian hinted at this potential since this morning, but had low forecast confidence in the timing and speed of the transition to lesser cloud and precipitation coverage. Oh, well. && .SHORT TERM...(Tonight through Monday night) Issued at 300 PM CDT Sat Apr 22 2017 With the 850 mb low east of the WFO PAH forecast area, the threat of thunderstorms has diminished greatly for the rest of this afternoon (first period). Latest GOES-R ("test" GOES 16) water vapor imagery from the 6.19 to 7.34 micron channels are still suggesting a slightly cyclonically curved jet axis (possibly two) oriented across the southern third of the WFO PAH forecast area. On the northern end of the entrance side of the jet, an increasingly sheared out closed low is still evident over the St. Louis Metropolitan area, with a deformation zone and noticeable stretching occurring across southern Illinois into Southwest Indiana and Northwest Kentucky. With sufficient moisture still in place, felt it was prudent to keep measurable QPF/PoPs, and Weather in place until the low and deformation zone are shifted northeast of the WFO PAH forecast area through the early evening. Likewise, there is some northward propagation of moisture and jet dynamics across the southern Pennyrile and extreme southeast corner of the Purchase area of West Kentucky during the last hour. Will keep a gradient of higher chances of rain across this area through the evening, gradually shrinking the chances of rain toward daybreak on Sunday. Have been pleased with the Canadian (CMCnh) and higher temporal resolution GFS deterministic guidance last night and today (and even back to Thursday). Both depicted the zone of instability and the progression of the thunderstorms quite well this morning. Along with the regionally blended guidance, utilized the Canadian, GFS, and the high resolution NAM-WRF model family, as well as the ESRL HRRR guidance for the PoP/Weather/QPF of the departing system tonight. The NAM-WRF, HRRR, and GFS MOS guidance also did well with the initialization of temperatures into early next week, so weighted the current forecast closer to these values. After the last of the rain moves east of the area late tonight, dry conditions should prevail through Monday night. Sunday will be the transition day with respect to the rise in temperatures, as most of the insolation used to provide thermal gradients for mixing and sensible heat exchanges (evaporation of rain-soaked ground) and remnant cloud covers in the east. In addition, there will be the issue of gradually weakening cold air advection in the boundary layer to contend with as well early on Sunday. .LONG TERM...(Tuesday through Saturday) Issued at 300 PM CDT Sat Apr 22 2017 Forecast confidence is rather high into Thursday, then it decreases considerably heading into next weekend. Troughing will develop aloft over the Rockies and high Plains by Tuesday, which will take the primary storm track from there northeast to the Great Lakes. An initial storm system will push a cold front through our region Wednesday afternoon or evening, and there should be a nice coverage of showers and thunderstorms near the front. Heavy rainfall will be a concern with precipitable water values around 1.5" which is near the 99th percentile compared to climatology. A few strong to severe storms will be possible as well. There is quite a bit of variability in the guidance in the timing and track of the next storm system for Thursday night into Saturday. The 12Z GFS seems to be the outlier here, with a much stronger upper ridge off the Carolina coast, while the ECMWF and GEM are weaker and farther east. The result of the GFS solution for us is that the next storm system digs into the southern Plains, and pushes the front back well north of our area by Friday. The other models trend farther south with the storm track, more over our region heading into next weekend. We will keep the PoPs mainly at or below 50% for most of the area Thursday night into Saturday, and wait for more of a consensus in the details. Temperatures will generally be warm in the absence of convection and associated cloud cover. Tuesday will see many locations approach 80. The GFS-based MEX guidance has a high of 87 in Paducah on Friday, which gives an indication of just how warm we could be if the front lifts back to our north. && .AVIATION... Issued at 725 PM CDT Sat Apr 22 2017 Low surface pressure over Dixie will roll away to the east overnight, while a sheared upper low to our northwest deepens and dives into TN. After sunrise, additional low surface pressure may develop over central TN in response. This should keep the pressure gradient across most of our region during the day with little change in wind direction. Winds may gust above 20 kts out of the north northeast by then. Any MVFR cigs are expected to go VFR soon, except for in the Pennyrile region of KY, where they may hang on for much longer. && .PAH WATCHES/WARNINGS/ADVISORIES... IL...None. MO...None. IN...None. KY...None. && $$ UPDATE...Smith SHORT TERM...Smith LONG TERM...DRS AVIATION UPDATE...DB
Area Forecast Discussion
National Weather Service Blacksburg VA
1009 PM EDT Sat Apr 22 2017 .SYNOPSIS... A frontal boundary will stall out across our area through Sunday with a wave of low pressure moving along it. Low pressure will slowly track along the front through the Tennessee Valley and into the Carolinas. The front moves southeast by Monday, with high pressure building in Tuesday. && .NEAR TERM /THROUGH SUNDAY/... As of 1000 PM EDT Saturday... Convective threat is over, now we move into the flood threat of this large-scale synoptic system. First, the backdoor/wedge front has slide generally south and southwest of the CWA, with the possible exception of the far southwest corner of the CWA. Solid cloud cover and rainfall will ensure that this remains in place until the large-scale synoptic system moves out of the area Tuesday. The upper low that will be the main culprit behind the evolving pattern is currently located across the western TN Valley. The low will intensify and deepen as southern stream short wave energy translates from the desert SW into the existing upper low. As the upper low moves into the Midsouth/Southeast Sunday night, it will take on a negative tilt, slow, and spin slowly in a northeastward direction from GA/SC to off the VA coast in the Mon-Tue time frame. Thus, the best dynamics for heavy rainfall and training of echoes will be in the Sunday night/Monday morning time frame. HRRR and radar trends suggest that rainfall overnight may tend to be rather meager, and likely less than was previously expected. Therefore, have decreased rainfall amounts some from what was previously indicated. All threat of thunder has ended. There may again be another lull in the precipitation Sunday morning until the next wave of heavier rainfall arrives Sunday afternoon. Again, the main concern from dynamics/synoptic support will not arrive until Sunday night into Monday morning. Heavy rainfall potential may linger into the area through much of the day Monday. Other than decreasing rainfall amounts in the near term, am not making any changes to longer term rainfall or the flood watch. Temperatures will remain unseasonably cool Sunday into Monday as the wedge persists and is continually reinforced with rainfall and solid clouds cover along with northeast flow. As of 450 PM EDT Saturday... Severe thunderstorm watch remains in effect until 9 PM this evening for southeast portions of Forecast Area. Flood Watch has been posted for midnight to Monday evening for most of the region. Frontal boundary continues to slowly drop south across the region this afternoon, before it stalls tonight into Sunday. Scattered showers and thunderstorms will develop ahead and along the front. With the instability and shear, a few strong to severe thunderstorms capable of damaging wind gusts and large hail will be possible this afternoon and evening. Localized flash flooding may be possible this afternoon into tonight with any training of thunderstorms with heavy rainfall. Look for a southward shift in convection this evening into tonight, then as next upper trough moves east into Tennessee. A surface low will shift to eastern Tennessee, then eastward to South Carolina by Sunday night. This will result in a northward shift in the rain with the wedge reinforcing. For pops used a blend of HRRR and NAM. Low temperatures tonight will range from around 40 degrees in the northwest mountains of Greenbrier county to the lower 50s in the Piedmont. Cloudy and cooler Sunday with occasional rain, heavy at times. As the rain continues to fall, the ground will become saturated and the potential for flooding will increase with time. The widespread potential starts at midnight tonight and continues into Sunday. High temperatures Sunday will be cool with readings from the upper 40s in the mountains to the mid 50s in the Piedmont. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... As of 440 PM EDT Saturday... The upper low tracks southeast and will be off the coast Monday night before making a turn to the northeast on Tuesday. Wedge at the surface remains in place through Monday night then pressure lower enough as the surface low reaches the North Carolina coast to bring winds around to the north then northwest and erode the wedge. Models showed a prolonged period of decent easterly winds which will aide in widespread to heavy rain Sunday night. The low is far enough offshore that a bulk of the moderate to heavy rain will move east of Lynchburg and Danville by Monday morning. However, there is enough moisture wrapping around the low that chance of showers in the foothills and piedmont extends through Tuesday. Stayed close to MAV guidance for temperatures through the period. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... As of 100 PM EDT Saturday... Brief period of upper ridging and higher 500MB heights Tuesday night and Wednesday. By then the long wave trough deepens in the central United States putting the region in broad southwest flow Thursday through Saturday. Models were showing varying degrees of strength of the southeast ridge. Low pressure tracking northeast into the Great Lakes will move a front into the Ohio and Tennessee Valleys on Thursday. This boundary stalls on Friday before another low moving out of the southern Plains pushes a warm front into the Ohio Valley on Saturday. This pattern keeps the rain potential to the west of the Mid Atlantic states. Temperatures will be above normal Wednesday and Thursday. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/... As of 750 PM EDT Saturday... Poor aviation conditions expected through the TAF valid period. Upper low across western TN will move southeast into GA, then slowly light northeast with a negative tilt Mon-Tue to off the Mid-Atlantic coast. High pressure anchored over the northeastern U.S. will combine with the upper low and surface low pressure to the south to result in a prolonged period of widespread rain, low clouds, and induced fog across the forecast area through the TAF valid period and beyond. Look for IFR-LIFR cigs generally in place at all TAF sites through the TAF valid period. Visibilities will be dependent on areas of heavier rainfall, but prevailing MVFR visibilities in -RA BR can be expected, with periods/pockets of IFR visibilities. Higher terrain will see more prolonged periods of IFR and even LIFR visibilities, but for the TAF sites proper, generally MVFR visibilities are expected through the TAF valid period. Winds will be NE 7-10kts with low end gusts likely across the Piedmont through the TAF valid period. High confidence in cigs through the TAF valid period. Medium to high confidence in vsbys through the TAF valid period. High confidence in wind dir/speed through the TAF valid period. Extended Aviation Discussion... Poor aviation conditions expected to continue through Monday. Some improvement will begin late Monday, but more likely into Tuesday as the upper low moves northeast of the area and the surface winds come around to the northeast as opposed to the northeast. This will allow ceilings to improve to MVFR and visibilities to VFR as the rain comes to an end or at least becomes much more showery in nature. VFR conditions are expected Wed-Thu as high pressure, but surface and aloft, build over the area. Another weather system will bring showers and possibly thunderstorms into the area late in the week. && .HYDROLOGY... As of 330 PM EDT SATURDAY... Flood watch has been posted for much of the region from Midnight tonight until Monday evening. Despite the semi- wet week, antecedent conditions are fairly dry across the eastern 2/3 of the CWA and generally about normal in the west. Moderate drought is still depicted on the U.S. Drought Monitor across much of the piedmont and Abnormally Dry over most of the Blue Ridge and surrounding area with near normal conditions in the west. This suggests that we can absorb more water than might be typical. 3-hour flash flood guidance from the River Forecast Centers ranges generally from about 1.5 inches in the west up to around 3 to 3.5 inches in the west, reflecting well the drier conditions east of the mountains. A slight risk for convective rainfall exceeding flash flood guidance was issued by WPC earlier for Day 1 and Day 2. Pockets of minor advisory-type flooding cannot be ruled out in convective storms which will be more likely tonight and Sunday and further south in the CWA where instability may be much higher. Any training convection over the same basins could produce pockets of flash flooding. At this point the river forecast is purely QPF based. Model QPFs have shown some decent run-to-run consistency over the last few cycles providing more confidence that this will fulfill expectations. Current WPC QPF in the day 1-3 period (this afternoon through early Monday) period is generally about 2 to 4 inches, with the bulk of it falling Sunday and current WFO grids are close to these numbers. The prolonged nature of the rainfall (48 to 72 hours) will lessen the risk of serious river flooding (and flash flooding) as runoff will be more spread out and less efficient. The two best St. Louis University CIPS analogs to this event are April 9-12, 2003 and March 28-30, 2010 both of which featured upper lows over the southeastern U.S. Both events resulted in minor to moderate river flooding on the Dan River but not on the New, James, upper Tennessee or upper Roanoke Rivers. Ensemble river forecasts from the GEFS ensemble are also highlighting the Dan and portions of the Roanoke basins as the most likely to flood, suggesting a greater likelihood for moderate or higher flooding but the NAEFS has been consistently showing lower probabilities. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Flood Watch through Monday evening for VAZ007-009>018-022-023- 032>034-043>046-058-059. NC...Flood Watch through Monday evening for NCZ001>006-018>020. WV...Flood Watch through Monday evening for WVZ042. && $$ SYNOPSIS...WP NEAR TERM...KK/RAB SHORT TERM...AMS LONG TERM...AMS AVIATION...AMS/KK/RAB HYDROLOGY...KK/MBS/PC