Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/31/20

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
516 PM CST Wed Dec 30 2020 .UPDATE... Issued at 512 PM CST Wed Dec 30 2020 Adjusted sky grids with a lean toward the HRRR given the latest trends on satellite with the stratus. Otherwise, no major changes are planned to the current forecast. && .SHORT TERM...(This Evening through Thursday Night) Issued at 314 PM CST Wed Dec 30 2020 We`ve seen a gradual eroding of a broken stratus deck from west to east through the day, and that trend should continue through tonight leading to mostly clear skies. While winds have been gusting upwards of 35 mph throughout the day across the Prairie Coteau, they will be diminishing this evening as a sfc high pressure axis continues eastward. Given the favorable conditions and fresh snow pack, low temperatures have been dropped to the lower end of guidance with single digits possible for much of the area east of the Missouri River. While not in the forecast due to low confidence, fog could develop tonight in favorable areas (limited to no snow melt today has contributed little to low-level moisture). Thursday begins with a pocket of elevated southwest winds aloft, and so relatively minor downslope winds may develop on the leeward side of the Prairie Coteau through the afternoon. Drifting of snow will be possible therefore as well during this time. Light breezes and mostly sunny skies are expected for the rest of the area, as a warm front lifts northeast through the day. High temperatures will be held down some by the snow cover, but will still be above average in the mid 20s to mid 30s. .LONG TERM...(Friday through Wednesday) Issued at 314 PM CST Wed Dec 30 2020 The oft-split flow pattern continues to dominate with only minor/weak upper trough passages Friday and Sunday mornings, with little to latch onto for precipitation chances. These features will aid in mixing however, and without any major cold intrusions we will see mostly above normal temperatures (though our recent snow pack may have some local impact). Nothing really else of note for the extended. && .AVIATION...(For the 00Z TAFS through 00Z Thursday Evening) Issued at 512 PM CST Wed Dec 30 2020 Terminals KABR,KATY,KPIR,KMBG MVFR stratus is expected to exit this evening. Will need to watch for any fog development toward morning, but otherwise VFR conditions and light winds will prevail. && .ABR WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. && $$ UPDATE...Wise SHORT TERM...Lueck LONG TERM...Connelly AVIATION...Wise
Area Forecast Discussion
National Weather Service Caribou ME
918 PM EST Wed Dec 30 2020 .SYNOPSIS... Low pressure will track northwest of Maine overnight. A cold front will cross the area Thursday morning. High pressure will cross the region on Friday. Low pressure approaches later Friday night then crosses the region on Saturday. High pressure will build in on Sunday before another low pressure passes south of the region on Monday. && .NEAR TERM /THROUGH THURSDAY/... 9:17 PM Update: Snow will continue to fill in across the area from Bangor north this evening. Temperatures along the coast have moderated significantly this evening with a 10 degree (F) rise at Bar Harbor Airport in the past couple of hours. Most areas along the coast are now in the upper 30s and lower 40s, so just rain expected. Bangor is about the dividing line between rain and snow with all snow expected in areas to the north of Bangor. A quick hitting system with most of the precipitation to wrap up by 12Z with the exception of Washington County. In the wake of this system, a cold front will cross the region tomorrow with snow showers a good bet across the north with the chance of a heavier squall. The latest BTV snow squall parameter does indicate a decent chance of squalls in the morning and early afternoon across the far north. Previous discussion: Clouds will continue to lower and thicken this evening w/snow arriving into the western areas and then spreading east through the rest of the night. Warm front will be lifting ne tonight w/some WAA noted. There is a strong mid level jetstreak of 55-60 kts as noted by the NAM and RAP as well some good llvl convergence. These two factors should be enough to generate some snow as the column moistens. Interesting enough, the high resolution guidance including the RAP/NAM and HRRR show the potential for some moderate snowfall across northern and western areas later this evening, and then a second area of higher QPF(snow) w/strong llvl convergence across the eastern side of the CWA. Steady snow is expected to wind down to snow showers/flurries Thursday morning as the best forcing will be moving off to the east and warm front lifts into New Brunswick. There is potential for up to 4 inches of snow across portions of the northern including Northern Penobscot and SE Aroostook County. Given the aforementioned setup, decided to go w/a Winter Weather Advisory through Thursday morning for MEZ001>006 which covers all of Aroostook County, Nrn Somerset and Nrn Penobscot County. Further s, less snowfall but a decision was made to boost snowfall totals by an inch given that the warmer air get pinched further s than previously forecast. This again is well shown by the NAM/RAP and HRRR guidance. Speaking of that warmer air, temps will warm up overnight w/readings by morning in the upper 20s to lower 30s. Downeast areas, especially the coast will see temps warm into the mid/upper 30s and this will allow for snow to rain to rain. Thursday will see a pre-frontal trof ahead of the cold front to slide across the region during the mid mrng hrs which will spark some snow showers across the northern and western areas. NAM soundings show some good shear of 35+ kts and some weak SB CAPE(RAP and NAM support the potential for some stronger snow showers and possibly a squall. Followed the midnight crew`s assessment of staying w/snow showers attm, but if the trends continue then a beef up in the forecast pops may be warranted. It will be rather windy w/sustained SW winds of 10-20 mph and gusts getting into the 35 mph range. This will especially be the case across the northern 1/2 of the CWA which could lead to some blowing snow and w/the snow shower and perhaps a squall could lead to rapidly changing vsbys. Temps will be falling during the afternoon as the cold front arrives into the region. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/... For Thursday night, cold air advection is forecast with high pressure building. Expect some subzero readings in the North Woods. Elsewhere, lows will be in the single digits north and teens in the southern half of the area. Could have to go a bit lower since the high is building so rapidly during the night...increasing the chance of winds going calm. Fresh snow cover will also help push lows downward. High pressure and sunshine is forecast for Friday with highs just above seasonal norms. Lows for Friday night will occur during the evening as temps drop quickly...but will remain steady later in the night as clouds increase ahead of Saturday`s storm. The Saturday storm will feature a southern stream shortwave pulling out of the Mississippi Valley and phasing with a fast-moving northern stream shortwave over the Great Lakes region. Surface low in the Great Lakes region will give way to a coastal low early Saturday afternoon. The questions are where the secondary does form and how fast...Gulf of Maine or along the Massachusetts coast. This has implications for both rain vs snow and amounts. More models favor the more southern track with the GFS as the northern outlier with a more amplified shortwave. Used a model blend to generate a more southern track than the GFS and pushed the rain/snow line a bit further south than our last forecast. This compromise track places the heavier potential banding from southern Piscataquis County towards southern Aroostook and northern Washington counties. This is where some low-end warning criteria snow is possible. However, a more southern track could drop the heavier snow band towards Bangor and Downeast...while reducing amounts in northern zones. This storm will be a fast-mover and will quickly exit the area Saturday evening. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... Snow ends Saturday evening and high pressure builds quickly during the night. There`s no significant cold air advection behind the low pressure system. A steep low level inversion appears likely as lows drop to the low teens north and upper teens to lower 20s in the south half of the area. Couldn`t rule out some patchy freezing fog given the moisture from Saturday`s event. The high continues in place Sunday with above normal temps. Things become interesting for later Sunday night into Monday as a southern stream cut-off low kicks out of the lower Mississippi Valley and propagates eastward. This time, phasing with a northern stream shortwave is not so clearcut. Some guidance has the cut-off harmlessly meandering out to sea south of the area while the ECMWF has been more consistent in generating a slow moving coastal storm. Since there`s very little cold air in place, coastal areas would be more likely to see rain. Have increased PoPs from our last package, but still mostly in the chance range north of the coast. The slow moving part could be a big concern as there will be plenty of moisture available if the Euro verifies. && .AVIATION /02Z THURSDAY THROUGH MONDAY/... NEAR TERM: Mostly IFR overnight at the northern terminals in snow...with IFR to low end MVFR at BGR/BHB in rain/snow, with mainly just rain at BHB. LLWS will also be a concern late tonight into Thursday morning w/a SW jetstreak of 40+ kts at 2000 ft. Sfc winds tonight will be out of the S at 10 mph. For Thursday, S winds to go SW 10-10 mph w/gusts of 35 mph. Snow will wind down to snow showers and flurries in the early morning at the northern terminals. Conditions will improve to VFR, but northern TAF sites especially n of KHUL could see MVFR and possible IFR w/some enhanced snow showers and perhaps a squall. Low vsbys and and some strong wind gusts could accompany this activity. && .MARINE... NEAR TERM: A south wind has rapidly increased this evening with near gale force gusts as of 9 pm. A llvL jet of 40 kts moving over the waters later tonight has the potential to mix down to sfc at 35+ kts. There is good alignment w/the winds from the blyr through 925mbs. Seas will respond accordingly building from 3-5 ft to 8 to 11 ft by early Thu morning. Rain will moving in later tonight. For Thu, SW 25-30 kt w/gusts 35-40 kt will shift to the W and subside to 15-20 kt by mid afternoon. There could be some gusts to 25 kt into late afternoon. Seas of 8-11 ft will be dropping back to 5-7 ft by late afternoon. Rain early in the morning. SHORT TERM: SCA conditions will continue into Thursday night and then return Saturday into Saturday night. There could be a few gusts to gale strength later Saturday. The next SCA starts Sunday night and continues into Tuesday morning. Gale force winds will be possible...and probable if a Noreaster does develop. && .CAR WATCHES/WARNINGS/ADVISORIES... ME...Winter Weather Advisory until 8 AM EST Thursday for MEZ001>006. MARINE...Gale Warning until 1 PM EST Thursday for ANZ050>052. && $$ Near Term...CB/Hewitt Short Term...MCW Long Term...MCW Aviation...CB/Hewitt/MCW Marine...CB/Hewitt/MCW
Area Forecast Discussion
National Weather Service State College PA
1030 PM EST Wed Dec 30 2020 .SYNOPSIS... A cold front will bring a band of light rain or mixed precipitation to the region starting late today across the Northwest Mountains, and occurring mainly as rain tonight elsewhere across Central and southern PA. A light accumulation of a coating to one inch of snow is possible across the Allegheny Mountains later tonight. High pressure then slides overhead for Thursday, making most of the day and evening dry with slightly above normal temperatures. Low pressure over the southern Plains will lift into the Great Lakes. This will force a large shield of mixed precipitation to overspread the entire state, likely holding off until Friday morning. A period of freezing rain is likely on Friday (New Year`s Day). The air will warm up slowly on Friday, turning the wintry mix to plain rain from south to north for most of Central PA. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... * Winter Storm Watch issued for a large swath of Central PA Friday into Friday night for potential significant accumulation of ice from Freezing Rain. Late evening discussion below. Cold front well to the northwest, and temperatures not real cold. Guidance temperatures not near freezing until later across the northwest, thus pulled snow out of most of the area prior to 06Z. Early evening discussion below. Minor adjustment so far as of 6 PM was to take out the snow early this evening, as so far just rain. While dewpoints lower to the east, the rain is still to the west. Thus still have a mix of rain and snow across the northeast later this evening. Will continue to monitor and adjust as needed. Afternoon discussion below. Low level warm advection ahead of a relatively weak cold front has led temperatures climbing to several to 10 degrees above normal this afternoon with the greatest departures occurring over the northern and western mountains where temps topped out around 40F. Latest RAP and 12Z HREFv2 indicate a 4-7 hour period of mainly rain late today and early tonight, followed by a 2-4 hour period when temps cool off enough to change the rain to wet snow with a coating to one inch possible in places like KJST, KFIG, KDUJ and KBFD. A gusty south to swrly breeze will remain through this evening before decreasing and shifting to the west-northwest in the wake of the Cfront late tonight. Min temps early Thursday will vary from the upper 20s north to mid 30s in the Lower Susq Valley. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/... The cfront will slip south and east be off to the east early in the morning, and cold advection will keep temps from rising more than 5F from their early morning values. The precip along and just in the wake of the cold front with the front will settle south of the MD border very early in the day and should stay there, leaving us with dry weather and slow clearing with gradually lifting cloud bases. Clouds will thin out to mainly cirrus or patchy altocu across the south toward dusk. && .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/... No major changes to the longer term, some light precipitation possible across the region late next week. Timing of the event for later this week, slower today, than yesterday. Detail listed below. Surface high pressure will move overhead Thursday and much of Thursday night bringing cold, dry air to much of central PA. The high centered over the Hudson Valley for Friday will be a good set up for cold air to drain down in from the NE and stay in place for a prolonged period. Meanwhile, a deep low will move from the Ohio Valley into the Great Lakes with WAA spreading northward across the region Friday, setting the stage for a significant ice event over central PA. Models have slowed down on the onset of precip, and it looks more likely that this will mainly be a Friday/Friday evening event. With precip and clouds arriving later, this will also give more time for radiational cooling to occur Thursday night with lows dropping into the teens north to 20s south, increasing the threat for frozen precip Friday. Although a brief period of snow or sleet is possible at the onset of precip, freezing rain will be the main threat as warmer air moves in aloft over the cold air trapped at the surface. WPC guidance and the NBM holds a significant (>0.25") accretion of ZR over the Laurels and along the Allegheny Front with the highest amounts over the ridge tops. Given the continued signals for significant ZR, we hoisted a winter storm watch earlier today for a large swath of the CWA. Most places should see temps rise above freezing Friday evening, but a few spots in the north may see temps linger near freezing into early Saturday morning. Behind the storm, Saturday looks mild across the CWA with highs in the 40s and 50s. A coastal system on Sunday may lead to some rain or snow for parts of the region, but heavy precip does not look likely at this point. Generally dry weather is expected the rest of next week. && .AVIATION /04Z THURSDAY THROUGH MONDAY/... At 03z, cigs have dropped to IFR at BFD in continuing light rain. Lower cigs and light rain showers will continue to slowly spread southeastward overnight as a cold front crosses the area. Widespread LLWS conditions are anticipated through the early overnight hours, as the surface flow slackens but a healthy S/SW low-level jet increases just above the surface. As colder air moves in, a changeover to light snow is expected overnight across the western highlands /BFD and JST/ along with IFR conds. Post-frontal low clouds (fuel-alternate/MVFR cigs), along with scattered flurries are expected at AOO, UNV, and IPT overnight. MDT and LNS could flirt with MVFR cigs overnight as well. Improving conds are expected on Thursday, as the front gradually sags south of the area. An active weather pattern will continue through the weekend, with additional rounds of precip expected on Friday and again Sunday. Outlook... Fri...Restrictions expected, with a wintry mix developing in the morning and transitioning to rain. Sat...Restrictions early with lingering low cigs. Gradual improvement by aftn. Sat night-Sun...Deteriorating conds, with light rain/snow developing. Mon...Lingering restrictions in -SHSN across western highlands. Becoming VFR elsewhere. && .CTP WATCHES/WARNINGS/ADVISORIES... Winter Storm Watch from Friday afternoon through late Friday night for PAZ005-006-010>012-017>019-037-041-042-045-046-049- 050. Winter Storm Watch from Friday morning through Friday evening for PAZ024>028-033>035. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert/Martin SHORT TERM...Dangelo LONG TERM...Lambert/Martin/Travis AVIATION...Evanego
details can be found in the long-term forecast discussion below.

Godwin && .LONG TERM... /Issued 334 PM CST Wed Dec 30 2020/ /Thursday Night through Wednesday/ The upper level low and its ejection out of northern Mexico and across Texas Thursday represents the primary uncertainty in the forecast. The trend in some of the models (Canadian/RAP/HRRR) today has been a slightly slower and subtle eastward shift of the track of the cyclone across our area. Based on some current water vapor analysis and a general 30dm NAM/GFS initialization error in the La Paz & Mazatlan RAOBs, it raises some concerns that this system still has the potential to veer off its forecast course. Any slower or more eastward track increases the potential for more wrap around snow impacting more of the CWA and for a longer time period Thursday night. Upper level troughs undergoing a shift from positive tilt to negative often do produce forecasting errors, because in general, the open wave will continue to drop equatorward until it reaches a baroclinic zone (or cold front). When it reaches the baroclinic zone it will strengthen, thereby distorting or "waving up" the horizontal temperature gradient. As warm air wraps around the northeast side and cold air dives southward on its backside the upper low will gain a poleward motion. The important thing to note about this process is that if the position of the cold front is not forecast well, then those errors cascade into impacting the ultimate track the upper low. In our current situation, the models have been trending the position of the cold front farther south - now showing it well into Mexico by late tonight - and the surface baroclinic zone has shifted from a forecast yesterday of Laredo to College Station to near the Texas coast. This makes sense as shallow cold fronts in Texas tend to head farther south than forecast, and the warm ocean waters will provide a natural baroclinic zone where the surface low will likely wrap up. Regardless of the exact track of the upper low, we expect widespread rain across the area early Thursday evening, but the atmosphere will be undergoing rapid changes as the low approaches and strong dynamic forcing overspreads the region. The upper level dry slot will first move northward and across the central and eastern zones during the evening hours with the widespread rain coming to an end. Very strong lift should cool atmospheric thermal profiles with mid level lapse rates increasing to 7-8 degrees C/km (good enough for isolated thunderstorms). Generally to the west of the I-35 corridor, this cooling will result in a thermal column completely below freezing. The change over from rain to snow will progress from the southwestern CWA northward during the evening hours - essentially following where the forcing is strongest ahead of the upper low. At some point across the central CWA, the pre-existing thermal profile will be too warm for dynamic cooling to get the column below freezing. While uncertainty is high regarding the eastward extent of the snow line, using the high res ensembles yields a reasonable looking snow forecast provided that the track errors discussed above don`t become too great. The western zones, generally along and west of 281 will be the primary location for accumulating snowfall. Snow is still forecast to mix in with the rain up to about the I-35 corridor late Thursday evening and overnight Friday morning. Right now we are forecasting 1-4" over the western zones, but acknowledge that very favorable dynamics associated with wrap-around precipitation events are in place. This could yield high snowfall rates of 2+ inches per hour and maybe even a stray rumble of thunder. Given the potential for more significant snow, but still hesitant to explicitly forecast more than 4 inches due to higher uncertainty, we have included a winter storm watch for Young, Stephens, and Eastland counties. Just to the east, an advisory will be issued for Lampasas county north to Jack county, and including Montague county. Later shifts can determine if a winter storm warning may be needed for the watch area or if an advisory will still suffice. The watch and advisory will start at 6 am to cover the low potential for light freezing rain Thursday, but it`s primarily for the evening and nighttime hours. Just to the east of the advisory counties (including the DFW Metro), some rain/snow mix should occur late, primarily associated with the wrap around band after midnight. Precip intensity looks like it will be lower here and surface temperatures should stay above freezing so accumulations should be insignificant and pose no travel issues in this region. Precipitation will rapidly exit the CWA by sunrise but post frontal clouds will hang around on Friday. Have gone with the cloudier MOS guidance and kept high temperatures on the cooler side of the envelope and only in the 40s. Clouds should finally clear on Saturday with a second upper level trough moving through the region. Fair and quiet weather is expected through Monday with highs warming a bit each day and lows in the 20s and 30s. The next upper system will bring more clouds and warmer temperatures to the region Tuesday and Wednesday. A few showers are possible mainly across the eastern and southeastern zones where moisture looks sufficient. TR.92 && .AVIATION... /NEW/ /00Z TAFs/ MVFR prevails this evening at TAF sites, but expect CIGs to fall to IFR later tonight as widespread RA continues to develop. Visibility will likely fall to IFR as well, particularly within heavier rainfall areas. There is a potential for intermittent LIFR CIGs during the day Thursday, but uncertainty is too high to mention in TAFs at this time. Gusty north winds will continue through the end of the TAF period. Just beyond the TAF period, RA may mix with or transition to SN across North Texas including at Metroplex TAF sites. This potential will need to be monitored closely, and a mention of RASN or SN may be needed in later issuances. Right now, no accumulating SN is expected in the Metroplex, which would keep impacts to ground operations at a minimum. Godwin && .PRELIMINARY POINT TEMPS/POPS... Dallas-Ft. Worth 36 44 35 45 33 / 80 100 90 0 0 Waco 39 46 35 49 31 / 100 100 50 0 0 Paris 38 46 38 45 32 / 90 100 90 5 0 Denton 33 44 32 44 28 / 70 100 90 5 0 McKinney 36 45 36 44 31 / 90 100 90 0 0 Dallas 38 47 38 46 34 / 90 100 90 0 0 Terrell 38 48 37 46 31 / 100 100 80 0 0 Corsicana 43 51 39 48 34 / 100 100 60 0 0 Temple 38 46 34 50 31 / 90 100 30 0 0 Mineral Wells 32 40 32 43 28 / 70 100 90 5 0 && .FWD WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch through Thursday afternoon for TXZ094-095- 105>107-120>123-135-146>148-161-162-175. Winter Weather Advisory from 6 AM Thursday to 3 AM CST Friday for TXZ091-101-116-130-141>143-156. Winter Storm Watch from Thursday morning through late Thursday night for TXZ100-115-129. && $$
National Weather Service Hastings NE
520 PM CST Wed Dec 30 2020 ...Aviation Update... .DISCUSSION...(This evening through Wednesday) Issued at 236 PM CST Wed Dec 30 2020 The main issues for this forecast is for dense fog and freezing fog potential Thursday night Friday morning and keeping an eye on a winter storm with a track that seems to be far enough southeast to essentially avoid impacts to our CWA. For tonight, I decided to put a little patchy fog in for our southeast NE areas for a couple of reasons. This seems to be a place where there was at least a little more melting of snow cover along the southern periphery of the newly fallen snow, but also the timing of the surface high gives us the lightest wind in this area as well. We may want to add points west if it looks like enough melting and/or wind looks like it would be light enough. The real issue for fog is for Thursday night and Friday morning as there is more potential for snow melt during the day on Thursday. Wind will have a north direction, but could be light enough to allow fog to occur. It will be cold enough that freezing fog could be an issue and make roadways slick. Still early though. I made a distinction toward where there would be recent snow cover over Nebraska, and little or none for Kansas. although there still was some signal for fog from SREF and HRRR, it was not as strong. For the winter system coming out of Mexico, the trends for snow/ice tracks continue to generally nudge southeast from the CWA. We clearly look cold enough to only have to worry about snow on the northwest shield of precip, but considering that convection to the south often nudges these tracks of precip farther south than model forecasts, I would not be surprised if our entire CWA misses out on this all together. Still kept low POPs in our southeast CWA, southeast of the tri-cities, but I can see this trending downward in future forecasts if trends continue with both ensembles and operational runs. The RAP really nudges this well southeast of the CWA, and I think it probably has the right idea. Some models are going for a double barrel solution where another upper low follows quickly behind the one tracking through on Friday, coming up on the weekend, but this low, if it develops as some models have advertised, should be far enough southeast to not be an issue for us. Looks like we will be cool to seasonable into next week as shortwave ridging tries to move in and we will get a little melting, perhaps each day. && .AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Friday) Issued at 518 PM CST Wed Dec 30 2020 VFR conditions are expected to prevail through this period. There is very low end chance for some patch fog early Thursday morning, but this is expected to stay to the southeast of KGRI and KEAR. Winds will be light, shifting to the south overnight into Thursday. && .GID WATCHES/WARNINGS/ADVISORIES... NE...NONE. KS...NONE. && $$ DISCUSSION...Heinlein AVIATION...Mangels
National Weather Service Jackson KY
1100 PM EST Wed Dec 30 2020 .UPDATE... Issued at 1100 PM EST WED DEC 30 2020 Updated grids to bring them in line with hourly surface obs. Seeing an honest uptick in rain shower activity across the area now as a surface cold front is just entering our area. Made additional adjustments to PoPs for recent radar trends - generally sped up the increase in poPs across the area. The surface boundary appears to have made it through Mt. Sterling and Morehead on its way east-southeast across the area this evening and may be on JKL`s doorstep. Am taking a close look at the 0Z runs as solutions come in, trying to determine if there is any threat for a wintry mix in the north. Forecast soundings and guidance suggest a solid drop in temperatures close to, or possibly to the freezing mark by dawn north of I-64, 32-34. And southwesterly winds aloft keep a deep layer (a few thousand ft) of warm air in place. Thus, by the strictest of definitions, can not rule out a period of freezing rain in the morning. Even the last several runs of the HRRR suggest the possibility. But have to believe any impacts would be nil with ground temperatures so far above the freezing mark and subsurface temperatures even warmer. Not even sure if any elevated or exposed surfaces would manage to get any ice accumulations without temperatures getting below freezing, and at this time there is nothing suggests that will happen. NBM 50th percentile does take temperatures in the northernmost portions of our forecast area down to the 32 degree mark, but considering other factors that may be too cool. Other guidance suggests lows bottoming out right at 33. But will keep an eye out in case some last minute adjustments to the forecast package are required should trends in updated solutions take us in that direction. UPDATE Issued at 725 PM EST WED DEC 30 2020 Surface cold front has made it into far western Kentucky, southeast Indiana and western Ohio. This feature will continue to slide eastward through the evening, tracking through eastern Kentucky roughly between 04-12Z. Rain showers will continue to spread eastward, with more steady rainfall expected later tonight. Steady rainfall will taper off to isolated showers for a period of time Thursday afternoon and evening, but returning Thursday night as another low pressure system pushes into the Midwest. Did need to make some adjustments to PoPs for this evening, bringing in activity a little sooner than originally forecasted based on current radar trends. Otherwise only made some tweaks to the hourly grids to bring them better in line with observations. && .SHORT TERM...(This evening through Thursday night) Issued at 328 PM EST WED DEC 30 2020 Strong southerly flow has continued this afternoon, ahead of a cold front pushing its way across the Ohio river valley this afternoon. We have seen a few wind gusts touch 35 mph, but overall, winds have remained just below lake wind advisory thresholds. The gusty winds will continue through early evening, before subsiding a bit as the strength of the mixing decreases. Temperatures have warmed into the lower 60s in most areas. The main focus for the short term is around the cold front as it pushes into and across the area tonight. Winds will shift a bit more southwesterly this evening, helping to transport better moisture into east Kentucky. The front will then push into central/northern Kentucky by late evening, with widespread rain expected along the boundary. The shield of rain will gradually shift south and east overnight, reaching far southeast Kentucky by dawn on Thursday. Mild temperatures will persist this evening, but should plummet pretty quickly as the front pushes south and east overnight. By morning, many areas will see temperatures sitting in the 30s with a persistent light rain. There is substantial warm air off the surface, even in the north, that will keep precipitation all liquid, essentially just leading to a very cold rain. The cold front will stall out along the VA/KY state line on Thursday, with low clouds hanging on north of the boundary through the day. While rain chances should gradually diminish from the north early Thursday, rain chances in the south and east could persist well into the afternoon. The cloudy weather and rain will keep temperatures fairly steady through the day, many locations likely not making it past 40. By Thursday night, we will be watching s developing low pressure system take shape across the plains with the stalled frontal boundary eventually lifting back to the north as a warm front. Southeast downslope flow should strengthen through the night with rain chances likely at a lull through much of the night. However, there is some weak diffluence aloft late (or almost 12z Friday), that may provide some support aloft for increasing rain chances prior to 12z. However, the forcing is weak and the southeast flow is quite strong. Thus, this may be a situation where we struggle to see measureable rainfall through 12z. The better chances may be in our western zones, closer to the better forcing. Temperatures may hold steady again overnight, and possibly increase late as the front starts to move back north. .LONG TERM...(Friday through Wednesday) Issued at 432 PM EST WED DEC 30 2020 A mild and unsettled pattern will be in place through Saturday night before quieter and cooler weather arrives for the first half of the new week. The 12z model suite is generally in good agreement agreement on the upper level pattern through Friday night. A few differences emerge over the weekend; but, with exception of the Canadian, agreement improves for the first half of the new workweek. The upper level analysis starting 12z Friday shows a stout ~590 dam high over the Bahamas with a ridge extending NW to over the upper Mississippi Valley. Another positively-tilted ridge extends from the California Coast to the northern US Rockies. A col, stretching from Nebraska to Utah connects the two ridges. To the south of the col, the first of two upper level lows is spinning over eastern Oklahoma while a second low is situated near the Arizona/New Mexico/Mexico borders. North of the col, a northern stream trough is passing over the Northern Plains. At the surface, ~1003 mb high pressure will be located over/near Arkansas with a warm front draped across the Tennessee Valley to the Carolina coast while the system`s cold front extends southeastward toward the Central Gulf Coast. The first upper low will skim along the northwest periphery of the strong southeastern high on Friday before opening into the northern stream trough passing the Great Lakes on Saturday. This will cause the surface low to lift toward the Great Lakes before weakening and transferring its energy to a coastal low near New England. A strong and very mild (10-12C @850mb) southerly 50+ knot 850mb jet will send the system`s warm front surging northward across the forecast area Friday morning. The trailing cold front will push in from the west by Friday evening but will falter as is crosses the Appalachians. As that first upper low fizzles, the second upper level low will evolve into a deeper low over the southern Plains before pivoting across the Ohio Valley and Great Lakes ahead of a deepening trough. This trough will continue to sharpen as it drops into the Southeast US and shunts the strong high near the Bahamas to over the Greater Antilles. At the surface, this second system will cause a weak, broad surface trough to develop late Saturday near the Mid-Mississippi Valley before consolidating into the a coastal low along the Carolina Coast early Sunday morning. As this occurs, a sub 0C 850mb air mass will arrive/develop along the back side of the system. As this second system departs, flat upper level ridging builds eastward to over the Ohio Valley Monday and Tuesday with attending surface high pressure. Another trough approaches from the west mid-week but models differ on the details. In sensible terms, widespread rain showers are expected to lift northward with the warm front Friday morning. Immediately downwind of the Cumberland Mountains, southeasterly downslope flow will likely keep the rain lighter. Once the front passes, a dry slot wrapping into the system should allow partly to mostly sunny skies to develop during the afternoon. The combination of sunshine and warm southerly breezes will easily send temperatures soaring into 60s. That breeze could become rather gusty, especially if skies clear faster, and may need to be further examined by later shifts. By late Friday, the NAMNEST shows a line of convection forming to our west with the approaching cold front, but this activity will likely start to dissipate due to waning instability as it pushes into eastern Kentucky. Most of the models show the the front faltering to our east Friday night with only slightly colder air filtering in for Saturday. Thus, high temperatures could again warm well into the 50s on Saturday under partly to mostly sunny skies. Rain showers are expected to redevelop Saturday night and persist into Sunday as the second upper level low passes near the Ohio River. Temperatures cooling below 0C at 850mb will allow for a changeover to snow across the highest elevations (above 3,000 feet) on Sunday before light precipitation tapers off. High pressure will follow Monday and Tuesday with partly to mostly sunny skies before clouds increase ahead of the next system on Wednesday. Sunday`s highs will be much cooler, ranging in the low to mid 40s. A slow warming trend ensues thereafter with highs reaching the low to mid 50s by Wednesday. Low temperatures will also be seasonably cool, ranging from the mid 20s to mid 30s from Sunday night through Tuesday night. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) ISSUED AT 725 PM EST WED DEC 30 2020 A cold front approaching the area and is expected to track through our forecast terminals between 06Z and 09Z. A large band of rain just ahead, along, and behind the frontal zone will slide eastward overnight, gradually dropping VSBYS and CIGS down into IFR territory by late tonight. South-southwesterly winds at around 10 kt with gusts to 20 kt or a bit higher have begun to show sign of decreasing in intensity. Expect this trend to continue over the next few hours, setting up a situation favorable for some non-convective LLWS as winds aloft (LLJ) remain higher, between 35 and 45 kts at H925 and as high as 60 kts at H850, all from the southwest. VSBYS improve late in the forecast window but CIGS remain low, in IFR range. && .JKL WATCHES/WARNINGS/ADVISORIES...NONE. && $$ UPDATE...RAY SHORT TERM...KAS LONG TERM...GEERTSON AVIATION...RAY
Area Forecast Discussion
National Weather Service New Orleans LA
921 PM CST Wed Dec 30 2020 .UPDATE... Forecast generally appears on track. While no significant changes were made to the 12-hr POPs, did make some tweaks to the timing of showers and storms for New Year`s Eve afternoon and night in the 3-hour POP blocks. Still looks like there will be potential for two rounds of storms with some convection well ahead of the main front and then a second round along the front. Main threats continue to be damaging wind gusts and tornadoes with hail being less likely. Safety tips: - Ensure you have multiple ways to receive severe weather warnings - at least one of which will wake you up since the severe weather threat will continue into the overnight hours - Know where your safe shelter will be if a warning is issued for your location. - The safest shelter location is a small, interior room on the lowest level of a well-built structure. Residents of manufactured homes should try to make arrangements for alternate shelter and plan to seek shelter in a sturdier building in the event a tornado watch or warning is issued. 95/DM && .AVIATION... Valid through 00z Jan 1... VIS satellite and area observations continue to indicate a broken area of low/mid-level clouds across a large portion of SE LA - generally along and west of I-55 which has brought CIG`s to around 06 to 08kft. Not anticipating any reductions in flight categories with VFR forecast for all area terminals through tonight. Otherwise, some patchy SCT/FEW low clouds will develop later today with persistent SSE to SE winds at the surface. A few isolated showers or storms will be possible along coastal Mississippi daybreak Thursday. However, coverage and intensity remains to be in question. If any activity does develop, temporary reductions in VIS, some lightning and gusty winds may be possible which would reduce flight categories at times. KLG && .PREV DISCUSSION... /issued 406 PM CST Wed Dec 30 2020/ SHORT TERM (This evening through Friday morning)... Plenty to talk about here in the next few days, so let`s dive right into it. Starting with late this afternoon evening with a quick current overview. As discussed with the morning update earlier, we remain largely in a prominent return flow/WAA pattern with deep- moist ascent in progress per comparing 00Z/12Z KLIX RAOBs (ascending base of subsidence inversion). Deeper moisture remains generally along I-55 on to the west where more low to mid- level clouds continue to be stuck in place. Mostly sunny skies continue just to the east with a few low-level Cu where mostly clear conditions should continue into the overnight hours. Additionally, have decided to go with a low-end Wind Advisory for SE LA parishes matching with LCH WFO as observations continue to indicate the strongest gusty wind potential caused by tightening and dropping MSL pressure gradient in the region. This should relax some by late evening/early tonight along with eventual decoupling of the PBL around and after the sun sets. Zooming out a bit taking a CONUS look at the synoptic pattern illustrates a very impressive and deep upper-low digging across northern Mexico, well south of the four corners region (around the order of 10 to 20dm lower than CFSR Climatology indicating an anomalously strong, deep low). Downstream of this, strong low-level winds continue across most of western and central Louisiana which has helped develop west of our area; pushing as far east as around BTR. This activity was collocated with an enhancement of the low-level jet which is quickly ejecting northward, and will drag any associated lift and shower activity into southern AR/central MS this evening. For us here locally, it will be mostly dry with blended guidance in good agreement keeping breezy southeasterly winds and a few clouds overnight. The first focus of any potential shower/storm chances comes early Thursday morning along or southeast of coastal Plaquemines parish; which CAM`s have been hinting at for a while now but has been pulling back a bit more on area coverage (especially latest HRRR trends) since better overall synoptic scale ascent remains well to the west. PoP`s have been trending higher in this location over the past few days, but given how CAM`s have been handling mesoscale feature better, have decided to trend PoPs downwards into the 20`s to 40`s along coastal MS where this potential cluster will eventually end up come around daybreak. Overall not too concerned with this cluster as deep-layer shear magnitudes are very limited, but will be closely monitored regardless as directional shear is there, and will warrant watching IF anything can develop in this region. Going into the morning hours on Thursday, the strong upper-low out west will press more towards the east into southern Texas, and eventually take on a negative tilt with rapid cyclogenesis across the SE TX Gulf coastline. We will see a lull in activity during this time frame (12Z to 18Z) but cant rule out an isolated shallow shower or two - especially near marine areas. Winds will be picking up out ahead of this deepening low as well, and will investigate the need for a Wind Advisory across our area in subsequent shifts tonight or early tomorrow. By around noon Thursday, we will begin to focus on what will likely be a quick ignition of showers and storms along a northward surging, weak warm front along and south of I-10/12 as deep-layer ascent increases, combined with some subtle fueling from diurnal destabilization with CAPE ranging in the range of 800-1200J/kg, MLCAPE in the 700-900J/kg range. An in-depth investigation with environmental soundings ahead of this disturbance from CAM guidance still shows a lag of higher magnitude deep-layer shear (0-1km SRH in the 100-150m2/s2 range/ 0-3km SRH in the 200 m2/s2 range). Given environmental hodographs and low/limited instability, not going to be too concerned with this initial wave just yet OR - any threat in the THU 18Z to FRI 00Z time frame may be limited. However, shear will be increasing hour by hour, especially in the 21Z to 03Z time frame and with any lingering pre-frontal convection, may evolve into an increasing threat. Regardless, any storm activity from this disturbance anchored across our CWA racing to the north will be closely monitored in this time frame. H5 temperatures in the -10.5 to -11.5 range will introduce a small hail threat, and any individual storm may contain damaging wind gusts. It is worth mentioning that sometimes, especially in our area, strong directional shear can sometimes overshadow the lack of shear magnitude, especially since we typically see shallow showers with low LCL`s along the coastline that may lead to quick, weak spin up tornadoes or waterspouts. This initial wave, by far, is not a substantial threat - but may evolve to become one especially by late afternoon and evening. As we continue into the evening hours, the next focus becomes the front itself racing quickly east and entering our far western CWA around 7 to 10PM. This is where maximized shear/forcing will reside with very impressive 0-1km SRH ranging 300-350+m2/s2, over 400+m2/s2 0-3km SRH. Environmental dry air entrainment will also push in along with the line helping to drag in much more impressive lapse rates in and around 6 to 6.5C/km (impressive enough for the northern Gulf coast). Storm motions will be very fast along what will likely be a very thin line of thunderstorms (anywhere on the order of 55 to 60kt individual storm motions bearing from 180/190). Overall threat timing along with the highest threat region will be for areas along and north of I-10/12 collocated with better shear, with timing from about 7 to 10PM for far western areas, to around 5 to 7AM across coastal MS as the line races east. Storm mode will include a thin QLCS with fast south to north moving embedded mesovortexes that may produce quick spin up tornadoes. Cant rule out a strong tornado or two especially in the Enhanced Risk area outlooked by SPC (10% TOR probs). However, overall forecast STP/EHI is not pinging on anything alarming given limited instability. A classing low CAPE/high shear environment that can sometimes over produce or under produce which leads to a low confidence forecast. Several things to consider here includes how much overall coverage will we see with the lead disturbance early Thursday afternoon. Greater coverage will limit any supportive instability and potentially cut off moisture supply to the area of best forcing, making for a real "pitiful" looking line - lowering overall severe risk. Shear is there in an event like this, but many mesoscale caveats exits that can lead to less of as risk. Additionally, CIPS guidance does hint at some historic events - one more notably December 28th 2015 (very similar synoptic scale set up) that did lead to a few small tornadoes. Good news is we will get this line out of here quickly early Friday followed by gusty winds out of the southwest and clearing conditions/cooler temperatures on Friday. LONG TERM (Friday through Wednesday)... After this system gets out of here, the next (slightly weaker) closed low embedded in a deep southern Plains trough rotates east across northern mexico, which will help keep upper-level flow out of the southwest. This trough swings across the region on Saturday, likely igniting a surface low and associated rain/storms well to our east giving us a re-enforcing shot of post-frontal cooler air. We will not see the coolest air until early Sunday morning with widespread mid to upper 30`s possible, aided by radiative cooling/subsidence caused by high pressure settling into the area. Highs will be generally seasonal, perhaps slightly below normal on Sunday but will moderate going into early to middle portions of next week. Not seeing any additional hazardous weather potential through the next 7 days which is some great news. Might see some light rain chances on Thursday with a weak impulse/shortwave trough rides along a quasi-zonal mid-level flow aloft. But overall, relatively quiet weather expected next week. But things can change. We will keep you posted. KLG MARINE... Persistent southeasterly onshore flow is expected out ahead of a developing strong storm system to the west. Small Craft Advisories are in effect for a large potion of the area due to increased wind/wind gusts and increasing seas. We may see a temporary lull in gusty winds tonight, but will likely pick back up early tomorrow lasting through the overnight hours as a cold front races east across the region. A few strong or severe storms will be possible, with strong wind gusts greater than 34kts and waterspouts the main threats. A reinforcing front arrives on Saturday helping to increase northwesterly winds but will likely remain below advisory criteria for now. Quiet weather conditions will extend into early to middle parts of next week. KLG && .PRELIMINARY POINT TEMPS/POPS... MCB 61 74 52 65 / 10 70 80 0 BTR 62 75 52 63 / 20 80 90 0 ASD 61 75 55 67 / 30 80 80 10 MSY 63 75 57 66 / 20 80 80 0 GPT 62 72 58 68 / 40 70 90 20 PQL 60 75 58 69 / 40 60 90 30 && .LIX WATCHES/WARNINGS/ADVISORIES... LA...None. GM...Small Craft Advisory until 6 PM CST Thursday for GMZ536-538-552- 555-557-570-572-575-577. Small Craft Advisory from 6 AM to 6 PM CST Thursday for GMZ550. Small Craft Advisory until 6 AM CST Thursday for GMZ534. MS...None. GM...Small Craft Advisory until 6 PM CST Thursday for GMZ538-552-555- 557-570-572-575-577. && $$
Area Forecast Discussion
National Weather Service Omaha/Valley NE
923 PM CST Wed Dec 30 2020 ...Updated Discussion... .UPDATE... Issued at 920 PM CST Wed Dec 30 2020 We are starting to see some areas of fog, locally dense, in parts of the Platte River Valley where skies are mostly clear. RAP and HRRR model output suggest that fog will expand some overnight as it slowly lifts to the north and east through Thursday mid morning. Added mention of areas of dense fog to the forecast, but did not issue at advisory at this point. One may be needed yet though within the next several hours, depending on how widespread it becomes. && .DISCUSSION... Issued at 333 PM CST Wed Dec 30 2020 Temps range from mid-20s to 30F as of 21Z. Day cloud phase satellite imagery reveals Nebraska and Iowa covered in fresh snow. In fact, the national snowfall analysis shows the entirety of both states have received some snow in the past 72 hours. This snow will help keep temps low overnight as high pressure settles in. The clear skies, diminished winds, and deep snow pack will allow temps to slip into single digits for all but our far western CWA. It`ll be chilly under a bright December moon. Eppley`s forecast low of 7F for the 2020`s last morning would be only the the 14th time slipping into single digits this year. Some sub-zero lows are possible in low-lying areas. Have driven temps close to the 20th percentile of solutions. I`ve introduced patchy fog into the forecast for much of southwest Iowa, southeast Nebraska, and the Missouri River valley. Have been conservative, so this area may need to be expanded by the overnight crew. Thursday will be cool despite the mostly sunny skies. The low sun angle will be no match for the snow`s high albedo. Expect mid-20s to lower 30s. Patchy fog may develop on Thursday night, too. The main forecast concern will be the possible impacts of a powerful low sweeping in from Mexico of all places. As the low closes tonight, it will take a sharp turn north, following the jet`s path around a Caribbean high. The system brings an anomalous amount of moisture to Missouri and Kansas Thursday night and Friday. We would expect these values of precipitable water to occur in only about 10% of Decembers. As models converge on a solution, the expected gradient continues to tighten. Only 4 of EC ensembles suggested more than an inch of snow was possible in Omaha, but the 12Z run has all members dry. One in five indicate at least that much snow for Nebraska City, and a majority in Falls City. As it stands, we`re expecting a dusting or less for all but the the extreme southeastern counties in the CWA with 0-3" in FNB the highest possible total. Expect a tight northern cut-off on the snow as this abnormally moist airmass butts against some dry air from the north. This glancing blow should have the snow falling only between 3 am and 3 pm on Friday. A wintry mix is expected for parts of Iowa and Missouri, but remain outside the confines of this CWA. We`ll just see flakes. Return flow develops on Saturday, setting the stage for warmer temps for the weekend`s second half with melting snow expected after lunch each day next week. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 525 PM CST Wed Dec 30 2020 The area of stratocumulus extending from north to east of KOMA may be in the area for a few hours this evening, but then it seems like it should move off to the east. Fog should develop at mainly KOMA and KLNK, with KOMA with visibilities possibly under 3 miles. Any fog that develops should lift by mid morning, with VFR conditions and a southerly breeze the rest of the day. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ UPDATE...Miller DISCUSSION...Nicolaisen AVIATION...Miller
Area Forecast Discussion
National Weather Service Pocatello ID
755 PM MST Wed Dec 30 2020 .UPDATE...Have updated the forecast through the overnight hours to nudge the forecast more in the direction of both observational trends as well as 00Z high-resolution model guidance trends. The update was necessitated because snow showers had already entered the Sawtooths and Wood River Valley, and radar echos were capturing developing snow showers across the Magic Valley and south hills as well. The 00Z models, the HRRR specifically, have captured this trend nicely and have updated the forecast to reflect these trends. The recently developed snow showers should continue on an eastward trajectory towards the Snake Plain over the next hour or two before the main area of snow showers arrives across the eastern Magic Valley, southern Snake Plain and south hills after midnight. The latest high-resolution guidance indicate a re-intensification of a broad shield of snow showers as the mid-level trough approaches from the mid-morning through early afternoon hours. These snow showers are depicted generally along and east of a Twin Falls to Island Park line. Have nudged the forecast in this direction as well. The previous discussion follows. AD && .PREV DISCUSSION... /issued 133 PM MST Wed Dec 30 2020/ SHORT TERM...Tonight through Fri night. An incoming trough is packing some moisture and will leave some light to moderate snow accumulations in eastern Idaho starting this evening in the central Idaho mountains and before midnight spreading to the ID-WY border. The trend from the previous forecast this morning is only slightly higher, with 95 percent of the mountain/highland area receiving less than 6 inches of snow, and Snake River plain/eastern Magic Valley receiving 0.5 inch in the warmer Magic Valley to 3 inches in the north end of the Snake River plain. The associated front is expected to sweep through during the morning hours on Thu, but wind on either side of the front should stay light. There is some southerly wind tonight that will bring in a warm frontal inversion that could allow at least partial melting and then a partial re-freeze for a few hours this evening, making for icy conditions on roads and highways. The area most affected by this will be the Wood River valley and Stanley basin, and the eastern Magic Valley. This should be over by midnight for all locations. Much lighter snow falls during the day Thu, with only the area north and east of Ashton in the northeast corner of the forecast area receiving more than an inch; most of the rest of the eastern highlands could receiving 0.5 to 1 inch, and the central Idaho mountains, south central highlands, and the valley and plain locations getting less than 0.5 inch during the day Thu. Thu night will be dry, with the clearer skies and northerly airflow dropping temperatures 10 to 15 deg F from tonight`s lows, with single digits returning to the Snake River plain. A drier Fri should see temperatures about the same as Thu, then Fri night the next storm starts spreading cloudiness during the evening and a chance of precipitation for the northern half of the forecast area, but the brunt of this storm arrives in the extended forecast. This will put Fri night lows in the teens for the populated areas. Have re-issued the Special Weather Statement with an emphasis on the potential for icy road conditions in the west, and the heavier snowfall in the northeast. Did not add any forecast zones to the Statement. Messick LONG TERM...Saturday through Wednesday. A constant flow of moisture will lead to better chances of mountain snow and a mix in the lower elevations almost daily heading into next week. For Saturday, light precipitation is expected mainly for the Sawtooths and eastern highlands...although there is much smaller chance elsewhere. Sunday through early Tuesday looks very wet as we get a stronger surge of moisture potentially working east of the Cascades into our area. While the mountains look to see a fairly steady stream of moisture, the Snake Plain/Magic Valley should see breaks between each individual storm moving across the state during that timeframe. This will be a warmer and windy pattern. This will lead to a mix of rain and snow across portions of the Magic Valley and Lower Snake Plain. The wind MAY create some blowing and drifting issues at higher elevations. The caveat here limiting that would be a "wetter" snow vs powder. Snow amounts have been trending down a bit, but favored areas of the Sawtooths could see 5-10" with a little more than that in valley locations. For the eastern highlands, we could 3-7" for the Big Holes and Island Park area. For the Shoshone Lava Beds area, 1-4" is not out of the question. Elsewhere, downslope and warm temperatures will limit snowfall potential. These numbers are NOT SET IN STONE, as we will need to see just how much moisture ends up getting past the Cascades...and with these types of storms we usually don`t get a better picture until we get a little closer to the event. Another bigger push of moisture arrives sometime later Wednesday. Keyes AVIATION...Conditions have improved at all TAF sites through the morning, as we turn attention toward potential impacts from snow and lower ceilings through tomorrow. We are currently VFR, awaiting to see if the first band of precipitation actually falls enough to impact airports. It seems a little bit too dry for snow to fall, BUT we are still thinking some impacts are possible with this first round. Confidence is LOW for the first few hours, and IF it does start snowing, look for MVFR/high end IFR conditions. Trends are showing that impacts are more likely with the band of snow moving in later this evening through tomorrow morning. We are forecasting MVFR/IFR due to snow and low clouds with this band. The ban should clear SUN closer to sunrise with improving weather. The band should stay going through at least the morning hours at BYI, PIH, IDA and DIJ...with IFR conditions. We could see a brief dip to LIFR if snowfall temporarily increases intensity-wise. Conditions should slowly improve tomorrow afternoon. Keyes && .PIH WATCHES/WARNINGS/ADVISORIES... None. && $$
Area Forecast Discussion
National Weather Service Blacksburg VA
923 PM EST Wed Dec 30 2020 .SYNOPSIS... A cold front slowly approaches from the west tonight, stalling across NC Thursday afternoon. A strong low pressure area will move across the mid Mississippi Valley by Friday and into the Great Lakes Friday night. This system will bring another soaking rain to the area. && .NEAR TERM /THROUGH THURSDAY/... As of 920 PM EST Wednesday... Patchy fog overnight with only very light showers in far southeast Piedmont and also far western slopes toward morning. Zone of light showers has shifted east of the forecast area this evening and not seeing any reports of drizzle although there could still be some in pockets near the Blue Ridge of NW NC and SW VA. Patchy fog also pretty limited at 9pm and is forming more along Blue Ridge but expect will eventually show up in other locations along either side of the Blue Ridge overnight. Only made some minor adjustments for PoPs and temperatures based on latest observations but otherwise no notable changes for rest of tonight. Cold front still expected to approach western slopes by morning and weaken, with light showers reaching far western slopes between 5 and 6am. Still a sprinkle or two in far southeast Piedmont later tonight per latest runs of HRRR from what can be seen on regional radars moving north into south- central NC. Prev discussion as of 530 PM EST Wednesday... Patchy drizzle a fog started to work it`s way up the Blue Ridge in NC and otherwise lowering ceilings in a lot of locations due to increasing overrunning with low-level SW jet riding over the sfc high pressure. This is likely to keep spreading north a bit more after dark, especially along and east of the Blue Ridge, but there some indications that some mountain locations west of the Blue Ridge may even get some breaks in clouds at some point, with the exception of far west as weak frontal boundary approaches. In addition to adding some more areas of drizzle and fog this evening, reduced the lower elevation winds since there is little mixing going on at this point. Only the ridges still have gusts into the 20-30mph range and that should continue most of the night. No other changes at this point. Previous discussion as of 140 PM EST Wednesday... Shower threat increasing but no hazards anticipated this period Clouds increasing across southern Virginia from NC, with warm advection in the mid levels and in advance of a front that was located from Michigan to western TN this afternoon. The front tracks into our region Thursday. Models continue to paint 2 areas of higher pops, one over the coastal plains of NC with better low level flux of moisture and along the front from mid TN to the central Appalachians. There remains a lull between these two areas, so have trimmed pops back tonight into Thursday from especially along and either side of the Blue Ridge. Not expecting much in the way of rainfall tonight-Thursday, with better threat arriving late Thu night as the warm front starts to track back north in advance of the upper low over eastern Oklahoma/western Arkansas. At play is a wedge of high pressure centered over New York and temp profiles are mainly keeping things of the liquid variety. Some of the colder guidance such as the NAM have a couple hours around 5-8am Friday of potential ice/sleet in along the Alleghanys. But at the moment confidence is not high on this being impactful. Higher rainfall amounts will be situated from the NC mountains/foothills into the Virginia piedmont late Thu night, but overall amounts are looking a half inch or less. With plenty of clouds, temperatures tonight will be milder in the mid 30s to lower 40s. Southwest flow along the front Thursday and some potential sunshine will lead to warmer highs in the upper 40s to mid 50s west, to upper 50s to lower 60s east. Temperatures will drop close to freezing in the higher mountains of Bath/Rockbridge/Amherst Thu night, where a potential for light ice exists, with most in the upper 30s to lower 40s. Forecast confidence is above average on winds, and average on pops/temps. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/... As of 154 PM EST Wednesday... Some freezing rain or sleet possible early Friday along the northern ridges. High pressure will wedge south from New England into North Carolina Friday. A closed low tracking northeast across the Red River Valley of Oklahoma will push a series of disturbances with warm moist air over the wedge. The trend of the model solutions has been to push colder air into northern portions of the forecast area. Added the mention of a period of freezing rain and sleet for the higher elevations Friday morning. Then, most locations will transition to light to moderate rain Friday afternoon into Friday evening. The day 3 SPC Convective Outlook highlighted any severe storms will be south of our area. High temperatures Friday will range from around 40 degrees in the north to the mid 50s in the far west. Believe the models are too fast in removing wedge and elected to slow the exit of the precipitation Friday night. With a slower approach, low clouds, drizzle and fog will be in the area into Saturday morning. Low temperatures Friday night will vary from the mid 30s in the northern mountains to the upper 40s in the piedmont. Rainfall amounts Friday will vary from around three tenths of an inch to around an inch and a half. The model trends continue to be lower on QPF totals for this event. As the front moves off the East coast, a low pressure wave forms along it Saturday and sends showers back to the area Saturday afternoon into Saturday night. High temperatures will be mild on Saturday generally from the upper 40s in the northwest mountains to the upper 60s in the piedmont. Low temperatures Saturday night into Sunday morning will be in the mid 30s in the west to the mid 40s in the east. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 154 PM EST Wednesday... Weather fairly quiet for our region after Sunday showers. Low pressure will lift northeastward into the New England coast Sunday into Monday. Most of the precipitation will fall as rain Sunday. On the backside of the low center, colder air looks to arrive slowly limiting any snow to the higher ridges of Southeast West Virginia Sunday. High pressure and ridging will build north into the central Appalachians Monday into Tuesday. The ridge aloft will flatten on Wednesday, this will allow an upper trough and associated cold front to approach the Ohio Valley. Temperatures will be near normal during the long term period. Low to moderate confidence in the long term forecast. && .AVIATION /02Z THURSDAY THROUGH MONDAY/... As of 705 PM EST Wednesday... Ceilings will likely remain VFR at western TAF sites, BLF and LWB, most of the night, but otherwise MVFR and even dropping to IFR at LYH and DAN overnight with weak wedge and overrunning. Some brief light rain or drizzle is also possible mainly at DAN tonight. As a weak front approaches the western slopes of the Appalachians Thursday morning expect conditions to deteriorate to MVFR or perhaps briefly IFR with a few showers around, and then continue to drop to IFR ceilings during the day with a shower or two still possible as the front slowly pushes through but weakens. Not expecting an all day rain. In the east, MVFR conditions likely will prevail most of the day, but by close to evening they could begin to drop and again toward or below IFR with the chances for more widespread showers increasing. Winds will be light and variable at the TAF sites overnight, but gusty from the south along higher ridges, thus concern for low-level wind shear at all TAF sites given much stronger winds at ridge top level. These ridge top winds weaken somewhat by morning thus no need to carry low-level wind shear during the day, and surface winds will generally remain light and variable with weakening front or surface trough overhead. Forecast confidence is moderate on at least having sub-VFR cigs by tonight at most/if not all taf sites, but low on how low cigs/vsbys will reach and threat of rain. Extended Aviation Discussion... MVFR/IFR conditions are expected through the end of the week as a wedge of high pressure moves in from the north and brings surface winds out of the northeast, especially in the Piedmont, by Thursday night into Friday. A strong frontal system will bring widespread rainfall to the region spreading over the wedge Thursday night and especially Friday. There is an increasing potential for freezing rain and light ice accumulations mainly along ridges as well for Friday, but potential appears low for any freezing rain at the TAF sites so far. Conditions remain unsettled with sub- VFR conditions and at least more light precipitation later in the weekend. High pressure should bring a return to VFR by Monday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...MBS/WP NEAR TERM...SK/WP SHORT TERM...KK LONG TERM...KK AVIATION...MBS/SK/WP