Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 240206 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 906 PM EST Thu Feb 23 2017 .SYNOPSIS... Weak high pressure off the Mid Atlantic coast will cover Virginia and North Carolina through tonight into Friday. A cold front will then sweep across the forecast area Friday night into Saturday, bringing chances for showers and thunderstorms. Temperatures will be unseasonably mild through Friday and may near record highs. High pressure returns to the forecast area on Sunday. && .NEAR TERM /THROUGH FRIDAY/... As of 900 PM EST Thursday... Cloud cover diminishing over the region this evening, but no fog as of yet with dewpoint depressions in the 5 to 12 degree range. Appears will still see fog per model soundings and residual low level moisture and higher dewpoints. However, fog will be not as dense as last night, but still noticable. Best threat of dense fog will be toward the piedmont east of Danville and Reidsville and possible portions of the mountain valleys. Otherwise, skies should be mostly clear to partly cloudy then some stratus forms with fog late. Lows will be in the upper 40s to lower 50s. Previous afternoon discussion... Ridge of surface high pressure remains in place across the forecast area. Sky conditions range from mostly clear to the east and mostly cloudy well to the west, and is contributing to a mild, spring-like afternoon. Current temperatures in several locales are near record highs for the date. Aloft, a positively- tilted mid-level shortwave ridge axis extends into the VA/NC piedmont region with a faster belt of mid-level southwest flow to our northwest in the Ohio Valley. For Tonight: Subsidence aloft along with stabilizing boundary layer will allow for diurnal cumulus clouds to erode. Though a few higher resolution models generate some token light PoPs west early tonight, I`m dubious about the prospect due to waning and already marginal surface-based instability, height rises in mid-levels and the light southerly weakly-convergent low-level wind field. Maintained a dry forecast, but I have also kept in the forecast of patchy fog primarily for eastern and central areas (east of the New River Valley to the Piedmont). Forecast soundings continue to reveal a developing radiational inversion along with light winds that are favorable for such development. I`m not as confident we`ll see fog as dense as last night given that we`re a day removed from the wetting rain, so we may not have as good near-surface moisture fluxes like we saw yesterday. I`ve therefore held on any Dense Fog Advisories with this package. Given good radiational cooling, lows should be warmest along the higher elevations (lower 50s) and coolest (mid/upper 40s) in the lower valleys and Piedmont. For Friday: Areas affected by fog stand to be several degrees cooler early in the morning but should burn off quickly under insolation. After that, we`ll be in the warm sector of a deepening surface low to our northwest over IL/IN. 850 mb temperatures are in excess of +10C - and off the 12z NAM are in the +12 to +13C ballpark. Dewpoints should be similar to today, though BUFKIT soundings show us capped to convection around 700 mb. Only the NAM-based guidance generates any token precip but given the cap aloft feel this is overdone and have again sided toward a drier forecast idea. Think we`ll end up seeing clear to partly cloudy skies with the greatest coverage of cloudiness more closely tied to orography, though. Will also see some increase in southerly winds/light breezes later in the day as pressure gradient starts to increase and low-level flow also increases. Used the warmer bias-corrected grids for high temperatures along with the 12z METMOS, which generates highs from the upper 60s to the upper 70s; a few spot 80 degree readings would not be out of the question in Charlotte, Pittsylvania and Caswell Counties. Since projected highs do get close to daily records in Blacksburg, I have added to the Climate section the high temperature records for Friday February 24th. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/... As of 338 PM EST Thursday... On Friday night, expect a south-southwest low level jet to be increasing in advance of an approaching cold front. While no precipitation is expected for the first half of the night, showers and some isolated storms in advance of the front will be arriving across the far western sections of the area by sunrise Saturday. The latest Day 2 Convective Outlook from the Storm Prediction Center places a marginal risk of severe weather across our far western tier of West Virginia and Virginia counties. Temperatures will be very mild with lows around 50 degrees to the lower 50s across the mountains, with low to mid 50s across the Piedmont. The front will cross the region on Saturday. Timing of this crossing has differed from run-to-run, and continues to demonstrate this with the latest 12Z/7AM solutions. The general consensus is for a pre- frontal line of convection to cross the area about three hours in advance of the actual cold front during the morning into the early afternoon. The front to cross late morning into the mid afternoon, and the associated 850 mb front to cross the area late afternoon into the evening. The latest Day 3 Convective Outlook from the Storm Prediction Center offers a marginal risk of severe weather across the central and northeastern sections of the forecast area with the passage of this front. Winds will be on the increase in the wake of this front, ushering in colder air by the afternoon, especially in the west. Anticipate early high temperatures with temperatures falling off in the afternoon. Eastern parts of the area will realized their high temperatures a little closer to the typical afternoon times, but still experience falling temperatures before sunset. Highs will range form the mid to upper 50s in the west, with lower 60s to near 70s across the Piedmont, with the warmest readings in this range across the far southeastern sections of the area. Lingering upslope showers across southeast West Virgina, south into the Northern Mountains of North Carolina will persist through the afternoon. Enough colder air will reach the highest peaks in this region for a mix with, or change over to, light now. This upslope activity will continue into Saturday night, but transition to more snow showers. Given how mild conditions will be prior to the arrival of snow showers, little if any accumulation is expected. Western Greenbrier County in West Virginia has the best chance for any measurable snowfall, with one-half inch possible. Low temperatures Saturday night will range from the mid to upper 20s across the mountains to the lower 30s across the Piedmont. The wind gusts at higher elevations may approach wind advisory levels at the highest elevations during the Saturday afternoon and evening time frame. However, most gusts across the mountains will be more in the 25 to 40 mph range with 20 to 30 mph across the Piedmont. Sunday into Sunday night, high pressure will build over the area, and shift east to the Atlantic coast. Expect no precipitation and limited cloud cover on Sunday. Sunday night, south to southwest winds will be on the increase again as the influence of the high pressure wanes, and another potential shortwave trough approaches from the west. Sunday, high temperatures will range from the mid 40s to near 50 across the mountains with low to mid 50s across the Piedmont. Low temperatures Sunday night will range from the upper 20s to around 30 across the mountains to the lower 30s across the Piedmont. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 338 PM EST Thursday... The biggest difference in the model guidance regards the precipitation potential on Monday. The GFS is agressive with a southern stream system heading northeast into the area on Monday, and impacting the entire area. The ECMWF is about 18 hours slower regarding this feature, with precipitation not arriving until after midnight Monday night. Our consensus forecast will continue to be just that. While it will reflect the quicker timing of the GFS, the magnitude will be downplayed a bit, and reflect guidance provided in the superblend solution. The onset of this precipitation has the potential for being a light wintry mix if the arrival is early Monday morning when surface temperatures are still at or below freezing over parts of the region. For now, will keep it simple with a rain versus snow forecast based upon surface temperatures below or above freezing. Through Wednesday, the region is expected to remain in a deep southwest flow in advance of a developing trough across the Central Plains states. The GFS continues to be more progressive in depicting pieces of energy streaming across the area, each with the potential for additional rounds of precipitation, especially on Wednesday. Our forecast will continue to reflect the superblend solution that accounts for these features, but on a diluted magnitude. Wednesday afternoon into Wednesday evening, the main upper trough and associated cold front are expected to race across the area. Look for another a line of convection to move through the region, with the potential for isolated thunderstorms. Gusty winds from the northwest are again forecast to develop in the wake of the cold front. Anticipate upslope rain and snow showers across portions of southeast West Virginia, south into the northern Mountains of North Carolina late Wednesday night, into and through the day on Thursday. Temperatures during this portion of the forecast will trend from near normal on Monday to around 10 to 15 degrees above normal for Tuesday and Wednesday. Thursday will be slightly cooler with readings around five degrees above normal. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/... As of 700 PM EST Thursday... Medium confidence in development of IFR/LIFR conditions toward daybreak. The region will remain under a lingering wedge remnant while one area of low pressure moves through the upper midwest, and another spins off the southeast coast. This pattern will keep a good amount of moisture in the boundary layer with a southerly wind flow. Expect diurnal convective clouds will wane and allow for a period of modest clearing, triggering development of low clouds and fog. Additional support for clouds will be advection of moisture up from the south and orographic lift along the Blue Ridge. This should all make for widespread IFR/LIFR in stratus and fog by daybreak at all sites, with the notable exception of KBLF as they are not a favored location for IFR/LIFR conditions in such a regime. This is a nuanced forecast largely dependent on behavior of lingering convective clouds early in the period so adjustments to forecast philosophy will be made as necessary. Any low clouds/fog will dissipate Friday morning followed by redevelopment of MVFR to VFR convective clouds by the afternoon. Precipitation chances tomorrow appear limited with a cap evident on model soundings. Winds will generally be light through the period with no significant gusts expected. Will continue to indicate AMD NOT SKED at KLYH due to persistent ASOS equipment issues. Extended Aviation Discussion... Band of showers and isolated thunderstorms with MVFR conditions arrive late Friday night into early Saturday along and ahead of a strong cold front. Drier weather and increasing northwest winds follow behind the front on Saturday afternoon through Sunday. Approach of another front Monday will provide increasing clouds and possibly showers and MVFR cigs to BLF/LWB late in the day. && .CLIMATE... As of 340 PM EST Thursday... Mostly sunny skies Friday may result in warm temperatures Thursday Night 2/23/17 Record Warm Lows: Bluefield 51 (1975) Danville 50 (1981) Lynchburg 52 (1925) Roanoke 54 (1925) Blacksburg 46 (1990) Friday 2/24/17 Record Highs: Bluefield 71 (1961) Danville 79 (2012) Lynchburg 79 (2012) Roanoke 80 (1985) Blacksburg 73 (1975) && .EQUIPMENT... As of 700 PM EST Thursday... The automated observation system at Lynchburg (LYH) continues to experience problems. Electronics technicians will investigate further on Friday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AL NEAR TERM...AL/WP SHORT TERM...DS LONG TERM...DS AVIATION...AL/MBS CLIMATE...WP EQUIPMENT...AMS

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