Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 180450 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1150 PM EST Sat Feb 17 2018 .SYNOPSIS... High pressure along the Mid-Atlantic Coast will shift off the New England coast this evening into tonight. Low pressure in Tennessee will rotate eastward tonight into Sunday. High pressure will build into our region Sunday. Warm front will move north through the area late Sunday night and early Monday providing clouds and a period of rain. && .NEAR TERM /THROUGH SUNDAY/... As of 1000 PM EST Saturday... Winter weather advisories have been cancelled as of 1000 PM. Adjustments made to PoPs as precip has moved through the region a bit faster than previously forecast. Any remaining precip in the region is quickly dissipating. Still maintaining some PoP along western ridges as upslope is likely going to continue to occur the next few hours. Slight adjustment to temps made to reflect current obs. Still expect a bit of an increase tonight for areas mainly south of 460 clearing kicks in a more normal diurnal trend for a few hours before sunrise. As of 300 PM EST Saturday... High pressure to our north providing enough colder air to result in wintry mixture of snow, sleet freezing rain and rain for our region. The greatest amounts of accumulating snow and sleet will occur along and north of Interstate 64. Wet snow accumulations of 2 to 4 inches, with localized amounts up to 5 inches, mainly higher ridges of the Alleghanys of Greenbrier and Bath counties and northward. The best chances for freezing rain will occur along the spine of the Blue Ridge mountain. Ice accumulations of a light glaze to up to two tenths expected along the Blue Ridge especially between Peaks of Otter and Fancy Gap. Temperature profiles will be the key to precipitation type this evening into tonight associated with low pressure center. In the north, colder air will allow for a mix of snow/sleet to remain around longer. The accumulating snow/sleet will be focus on the higher terrain, with less in the valleys and sleet will cut into totals as well. If there is a dramatic increase in QPF or stronger push of colder air may need to adjust headlines this evening into tonight. May need to monitor Greenbrier and Bath for potential upgrade depending on intensity. In the northwest, snow showers kick in behind the departing surface low off the coast with high pressure building into the Mid-MS Valley. For temperatures this evening into tonight, utilized an non-diurnal temperature curve and went with a blend of Namdng and isc continuity to capture the fall of temperatures with CAD and the rise of warm air pushing into the west outside of the wedge. For pops and weather utilized the Forecast builder with an ensemble approach with top down tool. In any case, light wintry mixture will transition to clearing east of the mountains overnight, and snow showers tapering off by dawn in the west. Also, there could be some freezing drizzle along the western slopes per model forecast soundings showing little if any moisture in the snow crystal growth temperature zone. Added some fog and drizzle to ISC grids. This may need to be expanded in AREAL coverage. Low temperatures tonight will range from the mid 20s in northwest Greenbrier county to the mid 30s in the Piedmont. High pressure to our west will build east across our region Sunday. This high pressure area will shift low-level thermal gradient at least briefly southward. Kept some morning stratus in the western mountains Sunday morning, then lift or burn off the clouds by Sunday afternoon. High temperatures on Sunday will vary from around 40 degrees in the northern Mountains to the upper 50s in the Piedmont. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... As of 300 PM EST SATURDAY... Warm front will move north through the area late Sunday night and early Monday providing clouds and a period of rain...QPF of a quarter /0.25/ or less. There may be a brief period of p-type issues around daybreak Monday with potential for freezing rain across Greenbrier and Bath counties, but confidence low and coverage limited per forecast early morning temperatures in the 32-36 degree range, and not yeilding enough values of 32 degrees or less to generate icing. Attm it appears clouds/rain will overspread our southern CWA shortly after midnight, and reach our northern CWA just before daybreak Monday, followed by partial clearing Monday afternoon as the warm front moves north of the area. Tuesday we will be well into the warm sector with unseasonably warm temperatures returning to the Mid-Atlantic States. An anomalous ridge of high pressure will become established just off the southeast Atlantic Coast, this feature resulting in very mild temperatures throughout the southeastern CONUS. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... As of 300 PM EST Saturday... Synoptic pattern features a strong subtropical ridge of high pressure parked along the southeast Atlantic Coast with 590+ heights at 500 mb. 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 second half of 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 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 Thursday. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... As of 1145 PM EST Saturday... Short wave crossing through the Ohio Valley will keep low clouds on the west slopes of the central Appalachians overnight. As a surface low develops off the Delmarva coast winds will become northwest and erode low clouds east of the Blue Ridge. Medium to high confidence on timing of improvement to VFR at KROA, KLYH and KDAN before 09Z/4AM. MVFR clouds will linger until around sunrise for BLF/LWB. Weak high pressure building into the region Sunday will maintain VFR conditions through the day. Winds will gusts up to 25 knots overnight but will diminish by afternoon. As the high moves offshore Sunday night, return flow of deeper moisture will bring rain back into the Mid Atlantic region after 00Z. Most area TAF sites will remain VFR through the 06Z end of the TAF forecast period. Extended Aviation Discussion... A warm front lifts back north into the area on Sunday night and Monday with another round of sub-VFR ceilings and visibilities with rain, 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. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...KK/WP NEAR TERM...JR/KK SHORT TERM...PM LONG TERM...PM AVIATION...AMS/JR is the U.S. government's official web portal to all federal, state and local government web resources and services.