Area Forecast Discussion
Issued by NWS Blacksburg, VA

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930 FXUS61 KRNK 162356 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 656 PM EST Fri Feb 16 2018 .SYNOPSIS... A series of upper-level disturbances will continue to track from west to east across the region over the next few days. Meanwhile, a Canadian cold front will move slowly southward through the region tonight, then stall across the Southeast. Light to moderate rainfall will accompany the front tonight. Then, an upper- level disturbance will bring a chance of wintry precipitation to the area Saturday as the cold air settles in place. Then early next week, a warm front will move back north bringing unseasonably warm temperatures to the area that will last several days. && .NEAR TERM /THROUGH SATURDAY/...
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As of 6:45 PM EST Friday... For the most part, forecast seems on track. Incoming high resolution guidance is trending toward slightly warmer than previously forecast, so nudged overnight lows up a bit. Adjusted PoPs to better reflect current radar and to dissipate near completely in the next few hours. As of 308 PM EST Friday... A cold front will drop southeast across the region this evening into tonight. A shortwave moving across the northern states will help to ensure that the front moves through the entire CWA and down into the Southeast States before it stalls during the weekend. Scattered showers noted on WSR-88d images ahead of and along the front boundary will move southeast across the region tonight. Utilized a blend of HRRR and Conshort will pops this evening, then shaped pops towards NAM tonight. As the front becomes parallel to the upper flow and encounters the strong upper ridge, it will begin to lose a lot of the associated precipitation. Low temperatures tonight are tricky and will depend on how far south the boundary pushes. In general, Lows overnight will range the lower 20s in northwest mountains of Greenbrier county to the upper 30s in the Piedmont. An upper disturbance will track northeast from the Mid-South and bring about a threat for wintry precipitation Saturday. Strong wedge will be in place across the region as shortwave and isentropic lift stream up over the top. As a result a wintry precipitation will spread northeast across the region on Saturday. Precipitation falling into the wedge with below freezing wet bulb temperatures will help deepen the cold air at the surface, while warm air aloft surges well above freezing. Ptype and amounts are a challenge in Saturday forecast. Expecting a mixture of snow,sleet, freezing rain and rain on Saturday. Total Accumulations with mixed precipitation are quite tricky as sleet/freezing rain greatly reduce amounts on the ground. Ground temperatures may also influence totals. Expect snow/sleet amounts to be generally in the 1 to 4 inch range with a glaze of ice. The heaviest snow will occur in northern portions of forecast area mainly north of I64 with 2 to 4 inches. The highest ice accumulation will occur along the Blue ridge mountains. Used the Forecast blender on Saturday to produce an ensemble Ptype and totals with complex temperature profiles. Utilized an non diurnal temperature curve on Saturday with high temperatures from around 30 degrees in the north to about 40 degrees in the south.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... As of 308 PM EST Friday... Cool wedge is forecast to linger through Saturday night with precip fading from west to east as the weather disturbance moves quickly northeast and away from the forecast area. Bulk of any lingering precip should be over by midnight with partial clearing after midnight. Winds will come around to the northwest by daybreak Sunday, downslope drying leading to fair weather and warmer temperatures for Sunday. Brief break Sunday will be quickly followed by increasing clouds and rain late Sunday night and Monday. The bubble of high pressure which rolls across the area Sunday will waste little time moving off the coast with return southwesterly flow allowing a warm front to move north through the area Monday. There may be some ptype issues around daybreak Monday with potential for freezing rain especially from the Alleghany Highlands through northern Greenbrier, but at this time the threat looks rather limited. A lot will depend on how fast the clouds move back in Sunday night and whether they will prevent temperatures from falling to near freezing. It is forecast to be plenty warm aloft with 85H temps of +4 to +7 deg C, so p-type favors rain unless the boundary layer temperatures can fall back to freezing. The warm front which moves through the area Monday will provide a 6- 12 hour window of precipitation with QPF of about a quarter /0.25/ to a half /0.50/ an inch...another beneficial wetting, but no flooding. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 300 PM EST Friday... Synoptic pattern features strong subtropical ridge of high pressure from the central/eastern caribbean up toward Bermuda. As a result, well above average mid-level heights are forecast across the eastern U.S. with values in the 582-588 DM range. Relative to climatology, this is 2 to 2.5 standard deviations above normal. This set-up favors much above normal temperatures for the Southeast States with the baroclinic zone forced to reside on the west side of the Appalachians from East Texas to the Ohio Valley and into the eastern Great Lakes. Repetitive rainfall is likely within this corridor during the week with our forecast area far enough east of the boundary to escape anything significant. Toward the end of the week, models hint that a surface front will impinge on the forecast area, but overall weather conditions for mid week feature above normal warmth and only a chance for showers pending any instability within the warm subtropical airmass. Temperatures Tuesday and Wednesday are expected to be 20-30 degrees above normal with highs in the 60s/70s and lows in the 40s. Models suggest potential for a backdoor front to impinge from the north- northeast Thursday, so somewhat cooler/wetter conditions are favored for the end of the week. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
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As of 1237 PM EST Friday... VFR conditions will start the TAF period at most locations as drier air moves in from the north. At the higher elevations of BLF and LWB MVFR or worse conditions will continue to be possible into the evening as any remaining showers in the area begin to dissipate. A wedge will begin to set up overnight, trapping the colder air at the sfc. An upper-level disturbance will pass over the region tomorrow bringing a shot of mostly cold rain into the region by the afternoon. Evaporative cooling into the drier layer at the ground will cause precipitation to become a mixed bag of rain, snow, sleet and freezing rain, mainly at higher elevations caught under the wedge. Ceilings and visibilities will drop to MVFR/IFR in precipitation. Winds at the onset of the TAF period will be from the northwest and slowing down from their late afternoon peaks, eventually becoming light and variable. During the day they will shift toward the east, topping out around 10 mph early in the day. Extended Aviation Discussion... Sub-VFR cigs/vsbys in rain or mixed precipitation will continue into Saturday night before VFR returns again on Sunday under weak high pressure. The cold/wintry weather will be brief as a warm front lifts back north into the area on Monday with another round of sub- VFR, especially mountains. High pressure strengthens offshore resulting in a return to overall VFR Tuesday ahead of the next cold front well west of the Appalachians. Scattered MVFR showers are expected Wednesday into Thursday.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...Winter Weather Advisory from 10 AM Saturday to midnight EST Saturday night for VAZ011-014-017>020-022>024-032>035. NC...None. WV...Winter Weather Advisory from 10 AM Saturday to midnight EST Saturday night for WVZ044-507-508. && $$ SYNOPSIS...KK/RAB NEAR TERM...JR/KK SHORT TERM...PM LONG TERM...PM AVIATION...JR/KK

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