Area Forecast Discussion
Issued by NWS Blacksburg, VA

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322 FXUS61 KRNK 220843 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 343 AM EST Wed Nov 22 2017 .SYNOPSIS... A cold front will cross the region this morning, all while an area of low pressure heads northeast off the Mid Atlantic coast. High pressure builds back into the area by Thanksgiving Day. Another cold front will cross the area this weekend. && .NEAR TERM /THROUGH TONIGHT/...
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As of 340 AM EST Wednesday... Upper trough and associated surface cold front to sweep through early this morning, frontal boundary at 08 UTC was nearing Blue Ridge already but with gustier winds still back in West Virginia. This is mainly a dry front with very light upslope precip along far western slopes, mainly very light snow showers behind front through the morning hours only. Low chances for any measurable precip however. Through about 5am scattered showers along western edge of baroclinic leaf from cyclogenesis just off of NC coast will still impact extreme southeastern portion of forecast area but will move east before day break. As western edge of mid cloud deck moves east and some clearing takes place, patchy fog is forming in foothills and this may temporarily spread east where it has rained overnight before winds behind the front begin to pick up and mix it out. Not sure how dense or widespread this will be so left it patchy and really just for a few hours mainly during the pre-dawn period. Otherwise for the day high pressure begins to push in from the west with clearing skies and gusty NW winds, as high as 25 to 30 mph along ridges, which gradually diminish by late afternoon. Far western slopes could see a flurry through the morning, mainly West Virginia, and skies will eventually clear there as well by the afternoon. With cold advection today and clouds lingering along far western slopes during the morning expect temperatures to rise only between 5 and 10 degrees by afternoon. East of the Blue Ridge temps should still climb into upper 50s to near 60 with full sun, although in most locations. Tonight a short wave weak upper ridge moves over with surface high pressure centered over the Appalachians by morning, and with clear skies this will allow for good radiational cooling and chilly night. Went closer to colder MET guidance for lows, with low to mid 20s mountains to upper 20s Piedmont.
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&& .SHORT TERM /THURSDAY THROUGH SATURDAY/... As of 226 AM EST Wednesday... An overall quiet holiday period in store with the area basically under weak high pressure within an upper split flow regime through the end of the week. Surface high pressure will keep the region dry for Thanksgiving, but cool under passing mid/high clouds as another weak northern stream shortwave trough boots across from the northwest. This along with the lingering 850 mb cool pool should interact with only light mixing to result in chilly highs in the 40s, to possibly a few warmer 50s east per weak downsloping and pending the degree of insolation given proximity of the wave off the southeast coast. Trough lifts out Thursday night into Friday with more zonal flow developing allowing surface high pressure to slide offshore. However guidance usually too fast to exit ridging in this setup at night which should result in another rather cold overnight under mainly clear skies as a weak extension of the parent ridge remains overhead. Thus went with lows on the cold end of MOS, mainly 20s, although may rise late along the ridges as warm advection starts to increase. Quick warmup then looks to ensue on Friday in response to increasing southwest flow behind the departing ridge and ahead of the next upstream 500 mb trough. Latest thickness values under sunshine support highs mostly in the 50s with values possibly reaching 60 southwest. Weak leftover subsidence region between the approaching upstream cold front and low pressure off the Carolinas will continue to get squeezed out Friday night despite lack of any phasing aloft. This should allow for some increase in clouds, especially southern and northwest sections but still dry. However continued mixing/warm advection should at least act to keep lows a bit milder with most seeing overall 30s with only the deeper valleys below freezing early on. With a mild start to the day and southwesterly flow increasing ahead of our next frontal passage, Saturday`s temperatures will warm above normal with readings in the 50s west to lower 60s east. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... As of 130 PM EST Tuesday... Fast split upper flow will again show more amplification to start the period with the translation of another deep 5h trough across the region next weekend. This should swing the next rather strong cold front across the area Saturday night and offshore on Sunday. Boundary again lacking moisture given low pressure off the Carolinas so mainly looking at perhaps a band of rain showers west late Saturday and increasing clouds elsewhere. This then to be followed by a few snow showers/flurries northwest mountains overnight into early Sunday as much colder air arrives. Flow should quickly flatten into early next week allowing for dry/sunny weather under moderating temperatures as surface high pressure slides overhead Monday and offshore into Tuesday. Mild high temps ahead of front with some 60s possible Saturday to dive back into the 30s/40s Sunday before slowly recovering to more seasonal levels by day 7. && .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/... As of 1220 AM EST Wednesday... A southern stream system anchored off the SC/GA coast and a northern stream short wave/cold front will impact the area tonight. Clouds and even light rain have spread across the Piedmont of NC/VA associated with the far northwestern fringes of the southern stream system. This precipitation along with MVFR ceilings and occasionally MVFR visibilities will continue for a few more hours, then shift east-southeast of the area. To the west, a narrow line of showers will accompany the approaching cold front, but most of these will largely dissipate before crossing the Alleghany front. Ceilings west of the Blue Ridge are mainly VFR, but will trend toward MVFR as upslope flow develops overnight behind the front. Rapid improvement to VFR is expected east of the crest of the Blue Ridge by mid-morning Wednesday morning behind the front. Sub-VFR ceilings may linger a bit longer along and west of a KBLF-KLWB line given the influence of lingering low level moisture and a northwest flow regime. VFR conditions should return Wednesday afternoon in the west. Winds ahead of the front will be SW 4-6kts becoming WNW-NW 8-12kts with low end gusts through much of the day Saturday behind the front, diminishing significantly around sunset. Medium to high confidence in ceilings and visibilities through the TAF valid period. Medium to high confidence in wind speed and direction through the TAF valid period. Extended Discussion... High pressure will provide for primarily VFR conditions Wednesday evening through Friday. A cold front will cross the area over the weekend. While primarily VFR conditions are still expected, some brief sub-VFR conditions are expected in the vicinity of the weekend front. Dry weather return Sunday night into Monday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RCS NEAR TERM...SK SHORT TERM...JH/RCS LONG TERM...JH AVIATION...RAB

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