Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 210546 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 146 AM EDT Tue Mar 21 2017 .SYNOPSIS... Weak low pressure will push east across the Appalachians overnight, triggering showers and isolated thunderstorms as a warm front lifts across the mid Atlantic states. As the low progresses east, a cold front will push south across the area Tuesday as high pressure builds in from the upper Midwest for the middle of the week. && .NEAR TERM /THROUGH TODAY/... As of 845 PM EDT Monday... MCV driven complex of showers and storms along the nose of the 850 mb theta-e axis continues to approach from the northwest this evening and expect the initial band to cross the mountains in the next hour or two. Appears main batch of more organized coverage will clip the northwest as well through midnight with a trailing line feature perhaps reaching the far southwest zones as well before fading. Just how widespread/strong the showers/storms will be remains iffy as evening soundings show support for elevated convection above the dry near surface inversion while surface instability remains about nil. Latest HRRR tends to fade coverage crossing the ridges but doesn`t have much of a handle on the trailing band to the southwest. Since more of a dynamic system would expect shra/tsra to go further than model guidance despite loss of heating. Thus upped pops a bit sooner to categorical northwest while extending the likelys farther south over the next few hours. Also appears feature will exit sooner after midnight with showers fading out east with possibly a few bands redeveloping far southwest where kept higher pops while trimming eastern half shortly after midnight. Some upward adjusts to temps overnight given moistening dewpoints with lows mostly in the 40s to around 50. Previous discussion as of 345 PM EDT Monday... Currently keeping an eye on a complex of showers and thunderstorms over central Indiana which are associated with a low pressure system that is advancing up the Ohio River Valley this afternoon. Weather forecast models are in good agreement that this low will pass across the central Appalachians overnight, with the associated showers and possibly isolated thunderstorms advancing to the Interstate 64 corridor shortly before midnight. Believe this convection will begin to diminish as it drifts southward toward the North Carolina/Virginia state line as winds in the wake of the cold front dragging behind the low shift increasingly westerly and downslope. Despite frontal passage, cold air does not yet truly enter the area, and overnight low temperatures will hold in the 40s nearly areawide. Through late Tuesday morning, expect residual rain shower activity to linger along the ridges of southeast West Virginia through the highlands of North Carolina, as well as in the vicinity of the passing cold front south of Highway 460 across the Piedmont. Latest forecast model solutions have become a little faster with the passage of the front, indicating less instability than previously called for along the southern end of the forecast area during the afternoon where temperatures are expected to rise into the 70s. Still, cannot rule out a slight chance of thunderstorms from late morning through mid afternoon across the south, though instability will be minimal. Scattering of clouds during the afternoon will promote high temperatures in the low/mid 70s across the Piedmont, while areas along and west of the Blue Ridge will hold in the 60s. && .SHORT TERM /TONIGHT THROUGH THURSDAY/... As of 300 PM EDT Monday... Models are trending faster and further to the south with a west-to- east oriented frontal passage Tuesday night. Even though models have most of the area dry by midnight, we decided to cut PoPs by half going from 60 percent to 30 percent. The highest PoPs remain along the VA/NC border south. The dew point front lags behind with the colder, drier air not entering the northern portion of the CWA (Lewisburg Wv-Lynchburg VA) until around sunrise Wednesday morning. Therefore, leaned toward the warmer MET guidance Tuesday night with most areas staying above freezing with the exception of higher ridges across Greenbrier County to the Alleghany Highlands. Moisture should be gone by the time cold air filters into the area Wednesday to limit accumulating snow to these ridges. High pressure will build in from the north Wednesday. The coldest air should not sink south until Wednesday evening as the center of the high wedges south across the piedmont. Wednesday temperatures will range from the upper 40s to lower 50s west to upper 50s-lower 60s east Wednesday. Cold air Wednesday night will send temperatures down into the mid to upper 20s across the forecast area. We will see uniform temperatures Thursday in the upper 40s to lower 50s as dry cool wedge engulfs the region. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 300 PM EDT Monday... Cool wedge of high pressure will begin to move off the VA/NC coast Thursday night. As the center of the wedge tracks east, a warm front will push moisture over the mountains which should only result in an increase in cloud cover Friday and Friday night. However, a bubble high will likely remain east of the Blue Ridge and over the foothills and piedmont counties into Friday night. This bubble of cool air and easterly flow will keep high temperatures east of the Blue Ridge close to 60F while the mountains warm into the lower to mid 60s. The wedge should be completely erode out of the region by Saturday afternoon with temperatures warming into the mid 60s to lower 70s across the forecast area. An area of low pressure is expected to track from the Midwest Saturday night towards the Ohio Valley Sunday. This system has the potential to bring severe weather to the region Sunday and Sunday night. The track of the system and timing of prefrontal convection into the region will be the biggest influence on how widespread severe potential may become. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... As of 135 AM EDT Tuesday... Radar showed a band of rain moving east, away from KDAN and KLYH. Another cluster of showers was approaching from West Virginia. SPC-HRRR has this precipitation weakening but moving across KLWB then KLYH by 09Z/5AM before dissipating. Boundary from southern Missouri into the southern Appalachians will be the focus for showers and thunderstorms today. Storms that develop over Tennessee will move east into North Carolina this afternoon and evening. Both front will continue to move south overnight and will be well into central and southern North Carolina by Wednesday morning. Northwest wind will combine with low level moisture to generate upslope MVFR/IFR low clouds mainly west of the Blue Ridge early this morning. The lower ceilings will hang in for most of the day over the mountains, while sites east of the Blue Ridge should become VFR this morning and remain as such through Tuesday. Extended Aviation Discussion... High pressure builds in for Wednesday which should improve ceilings back to VFR. By Thursday the high will wedge in from the northeast, so will remain mainly VFR. It is possible that residual lower ceilings may get trapped especially along and east of the Blue Ridge Wednesday night into Thursday, resulting in possible MVFR ceilings. Dry and warmer weather is expected on Friday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/NF NEAR TERM...JH/NF SHORT TERM...RCS LONG TERM...RCS AVIATION...AMS/JH is the U.S. government's official web portal to all federal, state and local government web resources and services.