Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 271733 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1233 PM EST Mon Feb 27 2017 .SYNOPSIS... High pressure over the area today will drift east as a weak upper-level disturbance passes to the north of the area by tonight. A warm front will lift north through the area Tuesday followed by a strong cold front late Wednesday. Cold high pressure will build in for the end of the week into the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 330 AM EST Monday... Canadian high pressure will drift east of the Mid-Atlantic seaboard by afternoon as a weak upper-level disturbance, embedded within the westerlies and ahead of a much stronger deepening disturbance in the western U.S. moves east-northeast from the western TN Valley into the OH Valley by Monday morning. With respect to precipitation, the main thrust of this system will be to our north, with perhaps a few sprinkles across the west and northwest parts of the CWA overnight into early Tuesday. As the system tracks to our northwest, the surface/boundary layer across our area will be fairly dry as a result of the antecedent high pressure system. The upper-level system will be north of the area by Tuesday morning. As the upper flow amplifies in response to the strong Pacific system moving inland, ridging in the eastern U.S. will push a warm front northward through the area Tuesday. This warm front will be located across northern GA into northern SC/southern NC by 12Z Tuesday. Patches of light rain will begin spreading northward through the counties along/southeast of the Blue Ridge by that time. Through this portion of the forecast period, QPF will generally be just a few hundredths of an inch at best and generally confined to areas south-east of the Blue Ridge with the warm front early Tuesday and/or west of I-77 with the weak upper disturbance later today/tonight. With respect to temperatures, expect a big warmup this period to well above normal temperatures as we move into Tuesday and Wednesday. Decoupling and radiational cooling, despite increasing cloud cover, has allowed many areas to drop into the mid and upper 20s this morning. However, this will be the last morning below freezing until the later part of the week. 850mb temps, starting out below 0C across most of the CWA early this morning, will quickly surge into the +12C to +14C range by Tuesday afternoon. This will yield high temperatures about 10 degrees above normal today and even warmer 60/70 degree readings for Tue and Wed. && .SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/... As of 330 AM EST Monday... Approaching long wave 500 MB trof and southeast ridging will result in broad southwest flow Tuesday through Wednesday when the next strong cold front comes through. No organized short waves but enough prolonged warm air advection and modest isentropic lift along with increasing moisture will lead to periods of showers. By Tuesday night precipitable water values are around inch. Maximum temperatures will be above normal on Tuesday and even warmer ahead of the front on Wednesday with 850MB temperatures closing in on +15C. Have kept minimum temperatures on Tuesday night on the warmer side of guidance, with the region still being in the warm sector. Models still show a spread in the timing of the front on Wednesday with the GFS the fastest, and roughly 6 hours ahead of the NAM. ECMWF was a compromise between the two. Similar to WPC recommendation, have leaned toward the NAM/ECMWF solution. This brings the front across the central and southern Appalachians between 18Z/1PM Wednesday and 06Z/1AM Thursday. Will have the highest probability of precipitation on Wednesday afternoon and evening. Winds pick up from the northwest behind the front with a 50 knot 850MB jet and pressure rises up to +10MB/6hrs. Will be increasing sustained winds and gusts in this time frame. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 330 AM EST Monday... A northern stream front moves across Friday morning. Appears moisture and lift will be further north of the forecast area, but some rain and snow showers could spill into the mountains of WV to the Alleghanys. Strong high pressure works in from the Midwest for Saturday, then shifts south across the southeast U.S for Sunday. After a period of cooler temperatures near to just below normal Thu-Sat, we will warm back up for Sunday. && .AVIATION /18Z MONDAY THROUGH FRIDAY/... As of 650 AM EST Monday... A weak upper-level disturbance will move from the northern Georgia toward the Carolinas through this evening. Mid and high clouds will accompany this feature with possibly a few sprinkles across the Alleghanys today into tonight. Confidence remains low of with the general location of the drizzle, so kept TAFs clear of any wx mentions through the period. Cloud cover will consist of a relatively consistent BKN to OVC layer through the period, but ceilings should remain above 5k feet, keeping VFR conditions for the majority of the period. Hints of sub VFR conditions late in the TAF period, but have kept MVFR plus until distribution gets a little more finite in future updates. A dry lower-level air mass should limit fog development overnight, even with hints of the ceilings breaking just after midnight in the KROA/KLWB/KLYH area. With Canadian high pressure moving off to the east of the region, winds will come around to the SSW- SSE through the period, at speeds of 5-10 mph, with some sporadic low end gusts possible by afternoon. Extended Aviation Discussion... A warm front across the southeast states will lift northeast Tuesday before passing to the north of the area on Wednesday. An increase in low-level moisture will likely result in increased likelihood of MVFR cigs Tuesday evening0, especially along and near the Blue Ridge with moist southeast flow. A few light rain showers may also accompany the front. A cold front pushes east into the area Wednesday into Wednesday night with potential for more widespread MVFR/IFR in showers and thunderstorms. A west to east moving squall line with strong to possibly severe thunderstorms, perhaps a QLCS type convective configuration, will be possible late Wednesday into Wednesday evening in advance of the front. Strong northwest winds along with mountain sub-VFR in upslope low clouds and light precip will likely follow the front for much of Thursday. Expect downslope drying to return VFR to eastern locations by Thursday afternoon with this trend lingering across eastern sections through the end of the week. However another weak clipper area of low pressure looks to track just north of the region by Friday with possible mountain MVFR in at least upslope cloudiness, and possible light precipitation western ridges later Thursday night into Friday. && .CLIMATE... As of 330 AM EST Monday... Record warm Mins for March 1 Roanoke.....52 in 1918 Lynchburg...57 in 1910 Danville....51 in 2012 Blacksburg..45 in 1997 Bluefield...56 in 1997 Record highs for March 1 Roanoke.....76 in 1972 Lynchburg...78 in 1918 Danville....80 in 1972 Blacksburg..72 in 1976 Bluefield...78 in 1997 && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RAB NEAR TERM...RAB SHORT TERM...AMS LONG TERM...AMS/WP AVIATION...JM/RAB CLIMATE...AMS

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