Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 230539 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1239 AM EST Fri Feb 23 2018 .SYNOPSIS... High pressure will remain off the Southeast coast into Friday, promoting above normal temperatures. A weak backdoor cold front will drop south tonight, then return north as a warm front late Friday. A stronger front will move through the region from the Ohio Valley this weekend. && .NEAR TERM /THROUGH TODAY/... As of 930 PM EST Thursday... Backdoor cold front continues to move south this evening. Evening soundings at RNK/GSO displaying some moisture below 7000 ft, but so far not much on radar. Isentropic lift should increase overnight to keep a low chance for light rain along and east of the Blue Ridge, mainly north of hwy 460. However, with moisture becoming shallower, drizzle maybe the precipitation type tonight. Overnight low temperatures will depend on how far the front moves south. Behind the front, temperatures will drop into the 40s, ahead of the front will be in the 50s. As of 620 PM EST Thursday... The backdoor front is starting to move into the area this evening. Temperatures at 6pm at Roanoke was 75F, Lynchburg was 54F and Charlottesville was 49F. This cool air will work south overnight. Light rain may accompany the front passage. Behind the front, low level moisture and easterly flow will keep low clouds, light rain, and drizzle in the area through Friday morning. As of 328 PM EST Thursday... A strong subtropical ridge of high pressure will remain anchored off the Southeast Coast tonight into Friday. Record warm temperatures this afternoon will remind everyone of Summer. A weak disturbance tracking around the northwest side of the upper ridge and an approaching back door front from the northeast may generate some showers across the northwest portion of forecast area mainly the Greenbrier Valley. Backdoor cold front will drop south this evening into tonight. This will introduce a cool wedge to areas east of the Appalachians. Have concerns this afternoon that the southern edge of low clouds have been eroding and lifting as it moves slowly south. The frontal boundary is expected to drop south and push down the Blue Ridge mountains. Then, the front will retreat northward Friday. For weather, initially started with convective showers then transition weather type to rain, drizzle and fog. Utilized a blend of the Conshort and NAM to capture the drop of temperatures with the frontal boundary. Low temperatures will range from the mid 40s deeper into the cool air to the mid 50s along the southern Blue ridge. Friday begins with areas of rain, drizzle and fog in the morning, then becomes scattered showers in the afternoon. Temperatures remain a challenge for Friday with a sharp gradient. How far south the front travels will be a key. High temperatures Friday will vary greatly from the lower to mid 70s outside the wedge especially in the western mountains and southwest mountains to the lower to mid 50s in the northeast deep in the relatively cooler air. && .SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/... As of 245 PM EST Thursday... Wedge of cool air should slowly weaken Friday night as a surface warm front lifts back northeast through the region before sliding well to the north on Saturday. May still see some spotty drizzle/fog linger in the northeast where the CAD typically holds longer espcly at night, otherwise mainly cloudy with steadying or rising temps in the 40s/50s overnight. Some small shower chance also far northwest as moisture spills over from the front west of the mountains but iffy at this point. Area slides back into the warm sector Saturday behind the exiting warm front and ahead of the main cold front that will approach from the west by Saturday night. This should set the stage for another breezy and very mild day with highs upper 60s to mid 70s under some sunny breaks. Again models attempt to generate scattered showers but likely overdone given slight height rises and focus of better lift well west of the mountains. Therefore lowered pops back to mainly chance far west/southwest and isolated elsewhere which may be generous. Cold front arrives from the west late Saturday night before slowly crossing the region in weakening fashion on Sunday. Appears a pre- frontal lobe of showers may reach the western sections late Saturday night but moreso Sunday morning with this swath of rainfall sliding east across the rest of the area Sunday. However models remain slower with potential for some splitting of the showers over the west with a jump to the piedmont later in the day where some instability will reside. Cant rule out isolated thunder far southeast so will leave in mention with high pops elsewhere for now, but with QPF of only a quarter to one half inch possible. Should be the last of the really warm days espcly if the boundary is slower so bumped up highs well into the 70s east, and 65-70 west similar to most extended guidance Mos. Front likely slow to exit the southeast Sunday night but degree of leftover deep moisture in question given a more progressive scenario off the GFS and brief drying seen on the latest ECMWF. However latest ensembles suggest that a few shower bands may hang on into the overnight espcly south and east until the actual 850 mb boundary crosses which wont happen until very late. This supports keeping in a 20/30 type pop across the region as the cool advection regime steadily increases overnight pushing lows back into the 40s most spots. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 300 PM EST Thursday... Upper flow will transition to a more zonal trajectory by early next week with weak shortwave ridging giving rise to a brief drier period early on before moisture returns by the end of the period. Could see some lingering showers espcly eastern/southern sections Monday in the wake of the exiting front from the weekend, as some solutions including the 12z ECMWF/CMC bring another weak wave up the front across the Carolinas. Therefore despite a lot of uncertainty will keep low pops mainly Monday morning along/southeast of the Blue Ridge before tapering from west to east in the afternoon. Otherwise models show high pressure building in by late Monday while remaining overhead Monday night before sliding to the coast on Tuesday. This should bring somewhat cooler and drier weather into Tuesday night with highs in the 50s/low 60s, which remains a good 10 degrees or so above normal. Fast west/southwest flow aloft looks to bring pieces of upper energy out of the southwest states by Wednesday with a couple waves ahead of a parent mid level system that will eject out into the upper Midwest by Thursday. This should result in an axis of deeper moisture lifting back north through the TN valley by early Wednesday and into our region Wednesday afternoon/night as a warm front edges north. Moisture remains in place well ahead of the trailing cold front that will approach Thursday with at least added showers around. Thus running with decent chance to low likely pops for mid week at this point. Highs again mostly 50s/60s with cooler values mountains Wednesday, and warmer readings possible Thursday east well ahead of the cold front. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/...
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As of 1230 AM EST Friday... The wedge, which most of yesterday was held up across central VA has surged southwest as expected this evening and generally is located from near LWB to BCB to MWK. Very shallow wedge will continue to filter southwest toward the SC/NC border by morning, then stall and begin to retreat back to the north Friday afternoon/evening. Little to no precipitation with or behind the wedge at this point, but would expect drizzle to develop in areas of favorable uplift, ROA/BCB/LYH, toward daybreak and into the morning hours along with MVFR visibilities in BR. Ceilings will stay in the low MVFR range much of the night, with isolated pockets of high end IFR. BLF may see low clouds/fog around daybreak with or without the wedge. Even though the wedge will begin to erode from the southwest by Friday afternoon, low-level moisture may remained trapped along and east of the Blue Ridge much of the afternoon/evening, so at this point, not expecting much improvement in cigs/vsbys through the afternoon/evening with the potential for low clouds and fog to develop again in the moist low-level air mass after 00Z Sat. Bottomline is generally poor aviation conditions through the TAF valid period with sub-VFR conditions much/most of the time. Winds will be east-northeast behind the wedge front, initially in the 10-15kt range with gusts to 20kts, decreasing toward daybreak becoming variable 5kts or less during the evening. Light southwest winds are expected to return to areas west of the Blue ridge by afternoon/evening. Medium confidence in ceilings and visibilities through the TAF valid period. Medium confidence in wind direction, medium to high confidence in wind speed through the TAF valid period. Extended Aviation Discussion... The backdoor cold front will stall along across North Carolina and retreat northward as a warm front toward Friday evening. Trapped low-level moisture will likely lead to widespread low clouds and fog with MVFR or worse conditions throughout Friday night into Saturday morning. VFR conditions are expected later in the day Saturday into early Sunday. Shower coverage and increasing likelihood for sub-VFR conditions can be expected later Sunday into Monday as a cold front approaches from the west. Sub-VFR conditions may persist into Monday as the front stalls to our south and an upper-level disturbance in the southern stream tracks across the southeast states along the front Monday.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...KK/PM NEAR TERM...KK/RCS SHORT TERM...JH LONG TERM...JH AVIATION...KK/RAB/RCS

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