Area Forecast Discussion
Issued by NWS Blacksburg, VA

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230 FXUS61 KRNK 071134 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 634 AM EST Wed Dec 7 2016 .SYNOPSIS... High pressure will build across the Mid Atlantic states today providing fair weather. An arctic front will cross the region Thursday, a much colder airmass overtaking the region for the remainder of the week. && .NEAR TERM /THROUGH TONIGHT/...
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As of 530 AM EST Wednesday... Beneficial rain from Tuesday will be followed by dry high pressure today. East of the Blue Ridge skies will be sunny with mild afternoon temperatures (50s). Clouds will linger across the mountains early this morning, erroding fore noon temperatures rebounding into the 40s. Changes will begin to take place tonight with clouds increasing ahead of an approaching arctic cold front. This front is the leading edge of some very cold air, originating from Canada and the blizzard stricken northern plains. Models hint of some very light precip (mainly trace amounts) associated with the arctic front with light snow showers western slopes and potential for a few sprinkles and/or virga along leading edge of the airmass change for the VA/NC piedmont toward daybreak Thursday. Temperatures tonight will dip into the 30s, which will be warm, relatively speaking compared to the temperatures that will occur the next several nights to follow.
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&& .SHORT TERM /THURSDAY THROUGH SATURDAY/... As of 430 AM EST Wednesday... Primary focus during the short-term period is the passage of the modified Arctic front and associated post-frontal, unseasonably cold air and breezy to gusty winds Thursday night and Friday. Daily details follow... Thursday: Trend in 00z model guidance suite continues to point to a dry frontal passage. The 850 mb front passing across the forecast area, reaching eastern Virginia by early afternoon. Expect cloud cover to erode rather quickly in the post-frontal airmass except in the favored southeast West Virginia counties where stratocu will be more difficult to shake free of. By the afternoon, period of strong cold air advection then begins as 850 mb temps fall to -6 to -12C. Moderately strong 3-hourly pressure rises during the 21-00z period along with northwesterly 850 mb winds of 35 knots supports increasing wind speeds of 15 to 20 mph, with gusts as high as 35 mph mainly across the hilly terrain. Highs in the 30s west of the Blue Ridge to the upper 40s/low 50s in the southeastern/southside Virginia areas, timing of which will be staggered to some extent by the passage of the front. In other words, trend in temps is pretty much all downhill once the front clears. Thursday Night: Thursday night stands to be one of the coldest nights yet experienced this early winter season, by all indications. Shallow moisture profile but enough in the -12 to -18C snow growth layer across western Greenbrier into northern Summers counties to support at least some light snow showers, but given the shallow moisture depth and limited progged lift in that layer, I suspect there won`t be much if any accumulation at all in these areas. Otherwise, variably cloudy skies with cold advection continuing in earnest. Conditions should stay relatively breezy as cold advection aloft should help to maintain relatively steep low-level lapse rates. Given low temperatures ranging from the teens to the mid 20s and winds of 15 to 20 mph, wind chills drop into the single digits to the teens. While not excessively cold, make sure to reach for the hat and coat as it should be the first cold evening thus far in the winter. Friday: Ridging continues to build in as center of large high pressure sets up over the Mississippi River Valley. Any leftover stratocu/areas of snow showers or flurries in southeast West Virginia should begin to burn off with the daytime sun. Though 850 mb temps begin to moderate to values around -9 to -13C, it will still be some 10 to 15 degrees colder than normal on Friday as highs temps only top out in the 20s west to the upper 30s/near 40s in the Virginia southside and the North Carolina piedmont. Friday Night: Large high pressure continues to advance east to near western West Virginia. While wind speeds should be lightening as pressure gradient relaxes, clear skies and dry airmass should allow for strong radiational cooling. Lows should dip into the teens to perhaps the low 20s areawide, but it wouldn`t surprise if some of the customarily colder locations such as Burke`s Garden drops into the single digits. Saturday: We should finally start to moderate temperature-wise with surface ridge and weak mid-level height rises aloft over the southern and central Appalachians. 850 mb temps on Saturday should run about -6 to -9C according to the GFS, which with abundant sun should push maxes into the 30s to mid 40s. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... As of 330 AM EST Wednesday... Stronger warm advection on southwest flow develops late Saturday night into Monday ahead of an approaching upstream cold front. Latest models have slowed down the eastward progression of deeper moisture with this initial front similar to the earlier ECMWF with most pops holding off until Sunday night or Monday. This should be after warming aloft has won out with mostly chance rain/showers with perhaps some snow mixed in far west/northwest. Lots of uncertainty moving ahead toward midweek in whether or not a punch of dry air follows this boundary before the next northern stream wave approaches Tuesday, or does it stall with moisture returning back north. For now will dry things out on day7 per WPC and latest 12Z ECMWF with overall temps 40s west to 50s north Monday/Tuesday. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
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As of 700 AM EST Wednesday... Trend toward VFR for all terminals today. Northwest wind flow has scoured moisture just east of Blue Ridge. Low Cigs/Vsbys still persist over eastern VA/NC, and along the western slopes of the Appalachians, but improving trend also expected for these areas between now and noon. For the 24 hour TAF Period 0712/0812... ROA...VFR. LYH...VFR. DAN...VFR, Tempo IFR VSBY until 14Z. BLF...MVFR CIG until 16Z, then VFR. LWB...VFR, Tempo MVFR CIG before 18Z. BCB...VFR, Tempo MVFR CIG before 15Z. MVFR CIG dvlpng aft 09Z Thu. medium to high confidence in ceilings, visibilities and winds during the taf period. Extended aviation discussion... An Arctic front will pass through the Mid-Atlantic Region Thursday. System is moisture starved, but still may produce a few rain/snow showers in advance of the boundary Thursday morning, and virga with potential for a few sprinkles across the VA/NC piedmont. After the frontal passage, cold blustery conditions will develop for Thursday night into Friday, with upslope snow showers along the western slopes of the Appalachians. MVFR cigs will be found across the mountains with VFR east of the Blue Ridge. Tempo MVFR vsbys will be associated with the -snsh. West to northwest winds behind the front will be strong into Friday with gusts likely topping 25-30 kts at times. Winds and any residual low level cloud cover should quickly fade by Saturday as high pressure builds overhead making for overall VFR conditions this weekend. Next weather system to follow will be a cold front, models suggesting a Sunday Night arrival.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PM NEAR TERM...PM SHORT TERM...AL LONG TERM...AL/JH AVIATION...PM

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