Area Forecast Discussion
Issued by NWS Blacksburg, VA

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397 FXUS61 KRNK 191758 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 158 PM EDT Mon Mar 19 2018 .SYNOPSIS... Low pressure over the central U.S. will move east today resulting in increasing cloud cover. This system will initially bring rain to the mid Atlantic Region beginning later today and lasting into Tuesday, but wintry precipitation will be possible Tuesday night into Wednesday as cold air wraps into the system from the north and west. Brief clearing is expected for the end of the work week with yet another storm system effecting the region for the weekend. && .NEAR TERM /THROUGH TONIGHT/...
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As of 145 PM EDT Monday... Enough heating through the high clouds to warm most locations into the mid 50s to lower 60s. Have adjusted temperatures for this trend. Clouds will be on the increase today as storm system over the central U.S. approaches our region. Models generate very little rain during the daylight hours, due to the lingering effects from Sunday`s dry airmass. However, can`t rule out a brief period of light rain until isentropic lift finally overcomes dry layers permitting widespread rain tonight. Low pressure to our west will track east and into our region for tonight...models suggesting a widespread wetting with between a half inch /0.50/ and one inch /1.00/ of rain. During this time frame (now through daybreak Tuesday), temperatures remain warm enough for all of the precipitation to fall as rain.
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&& .SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/... As of 400 AM EDT Monday... Progressive upper flow with an active southern stream will keep a steady stream of weather systems tracking across the region during the period with the threat of notable rainfall, perhaps a few thunderstorms, and then winter precipitation in the form of accumulating snowfall. A Miller B type scenario will evolve Tue-Wed as a southern stream low tracks from the TN Valley into the central and southern Appalachians, then migrates toward the SC/NC coast before moving offshore and intensifying into a potential significant noreaster later Wed into Thu. As the surface low tracks into the eastern TN valley Tuesday, widespread rainfall is expected with total liquid QPF of 1 to 1.5 inch by Tue afternoon/evening. As the surface translates first to our southeast, colder air will begin to filter in both from the west around the upper trough and also down through the Shenandoah Valley in a wedge fashion. The column will cool enough for precipitation to change from rain to snow in a top down fashion, mainly I-64 corridor and western mountains/higher elevations first, then working its way toward the Piedmont and east of the Blue Ridge after sunset Tue. With the March sun, warm ground, and initially above 0C 850mb temps until Tue afternoon from the north to south, feel that accumulations will be hard to come by until after the sun sets and the surface low moves to our east/northeast Tue night, again in a top down fashion. Higher elevations and further north have the best chance of seeing 1 inch or more of snow. Snow accumulations are quite problematic. First, ground temperatures are warm and will not be below freezing at the beginning of the event, and really only for a brief period Tue night/early Wed in most areas. Second, March sun will render accumulations difficult until after sunset Tue evening. Most of the snow accumulation will come as the upper low sags southward across the area and a deformation zone lingers over the area Wed from the slowly northward moving coastal system. Model snow accumulations are mainly in the 1-3 inch range, with the exception of the GFS, which just like last weeks snowstorm is double the other models, largely because it is double the QPF as well. WPC has cut snow amounts roughly in half and shifted a bit further west from earlier outlooks. Discussed the possibility of a watch and/or advisory with neighboring offices. While initially on board with a Watch for I-64 corridor and through the western mountains of the CWA down into northwest NC, latest WPC and most model guidance suggests warning criteria snow will not be met with this event, with amounts at advisory levels or less in most areas. This would be a 4th and 5th period advisory, so that decision will be deferred to the day shift. We feel quite certain that this event will net an advisory for a number of counties along/west of the Blue Ridge, but confidence in reaching Watch/Warning level criteria is too low to issue a 4th period Watch at this time. Will continue to highlight potential in the HWO/eHWO and DSS mediums until confidence increases. An advisory may well come out later today. Another concern as the coastal system/noreaster gins up will be strong northwest winds. This is evident Wed into Thu, much like the system of last week. Temperatures will be near normal Tuesday, but as the upper trough moves to our south and the coastal low develops, will drop to well below normal levels. 850mb temps in the core of the upper low will drop toward -6C in the Wed-Thu time frame. This will yield low temperatures in the 20s west to 30s east and highs in the 30s west to 40s east, about 15-20 degrees below normal. && .LONG TERM /FRIDAY THROUGH SUNDAY/... As of 400 AM EDT Monday... Active weather pattern is expected to continue with continued mostly below normal temperatures. Progressive upper flow will result in another fast moving/vigorous mid-latitude low pressure area reaching the CWA as quickly as Friday night/early Saturday. Once again, may be dealing with at least some threat of winter precipitation with this event with a lingering wedge of cool air in the wake of the preceding system and a warm front with good isentropic lift, lifting northward into the region Saturday. Most models are suggesting at least some period of snow/sleet mountains and northern I-64 corridor areas until temperatures warm into the 40s Saturday afternoon. The threat for winter precipitation may return again Sunday morning in the north/mountains. Temperatures will remain well below normal during this period once again. Lows mainly in the 20s west to 30s east with highs in the 30s and 40s west to the lower 50s east. && .AVIATION /18Z MONDAY THROUGH SATURDAY/...
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As of 145 PM EDT Monday... Mainly VFR this afternoon in southwest Virginia, northwest North Carolina and southeast West Virginia with a few spots of MVFR and light rain along the Virginia/North Carolina border. Widespread moderate rain will spread across the region from the southwest with MVFR to IFR ceilings. High confidence of IFR to LIFR conditions between 03Z/11PM to 09Z/5AM when lift and upslope is maximized. Primary batch of rain moves northeast of the area Tuesday morning. Moderate confidence that ceilings and visibility will improve to VFR after the rain ends on Tuesday. Next round of rain will move after the 18Z end of the TAF period. Extended Aviation Discussion... As a low pressure system heads offshore Tuesday night, precipitation wrapping along the western periphery of this system is expected to change to snow. This will result in MVFR/IFR conditions, and gusty north to northwest winds Tuesday night and Wednesday. Drier air should finally result in improving conditions Thursday as high pressure builds from the northwest. Another low pressure system will bring rain and the associated MVFR or lower conditions for Friday and Saturday.
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&& .EQUIPMENT... As of 340 AM EDT Monday... The Mount Jefferson NWR remains off the air and will likely be sometime this week before it is operational again. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PM NEAR TERM...PM SHORT TERM...RAB LONG TERM...RAB AVIATION...AMS/PM EQUIPMENT...AMS/JH is the U.S. government's official web portal to all federal, state and local government web resources and services.