Area Forecast Discussion
Issued by NWS Blacksburg, VA

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160 FXUS61 KRNK 271418 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1018 AM EDT Thu Apr 27 2017 .SYNOPSIS...
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Chances of showers and thunderstorms begin this afternoon as a low pressure system passes to the north. High pressure will build off the Southeast coast during the next few days to bring well above normal temperatures.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 1015 AM EDT Thursday... A low pressure system centered just north of the Great Lakes is stretching a cold front southward toward the Ohio River Valley. An outflow boundary from convection the previous day in this area should move ahead toward the Appalachian Mountains by the afternoon. High resolution models show scattered showers and thunderstorms developing over the Tennessee River Valley and spreading eastward toward locations west of the Blue Ridge. The Storm Prediction Center has the entire CWA outlooked for a marginal risk of severe thunderstorms today. Model CAPE is forecast into the 1000-1500 J/kg range this afternoon, but diurnal gains in buoyancy may be muted by increasing cloud coverage ahead of the cold front. If sufficient solar heating occurs, low to mid level flow will encourage momentum transport capable of supporting locally damaging wind gusts. Loss of daytime heating will result in a demise of the shower and thunderstorm activity before midnight. The actual surface front should dissipate overhead as the building upper ridge of high pressure acts as a road block to prevent any sort of change in air mass to the forecast area.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 400 AM EDT Thursday... A broad and strong h5 ridge will be centered over the southeastern U.S. in this period with 588 dm heights over Florida building to 591+ dm just off the Carolina coast by Saturday. This will provide a very warm and fairly humid air mass across the southern Appalachian region, especially for late April. High temperatures will run 10 to 15F above normal both Friday and Saturday with highs in the upper 70s to low/mid 80s Friday to mid/high 80s Saturday. Not really threatening records but still unseasonably warm. Precipitation-wise do not expect to see much, if any. A strong upper trough will be digging southward into the southern high plains Friday/Saturday setting the stage for a heavy rainfall event well to our west, across parts of the southern and central Mississippi Valley. Forcing for precipitation in our area will be weak with only a chance for diurnally driven convection which will be widely scattered and not hydrologically significant. This will allow the last of our flooded rivers to continue receding. Models indicate decent ML CAPE of 1-2K Saturday afternoon but only modest shear but could allow a few strong to near-severe pulse thunderstorms in the afternoon. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 400 AM EDT Thursday... Very warm and humid conditions continue Sunday with the chance for showers and thunderstorms, especially along the Blue Ridge. By Monday, the vertically stacked upper closed low over the Midwest will move into the Great Lakes region. This will push a vigorous cold front into the area from the west with a good chance of showers and thunderstorms through Monday afternoon into Monday night. High pressure will then build on for Tuesday with cooler weather and windy conditions. Moisture increases on Wednesday, with better chances of rain Wednesday night into Thursday. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... As of 745 AM EDT Thursday... VFR conditions at all sites through 18z/2PM today before frontal showers and a few storms arrive along the western slopes of the Appalachians. Increasing clouds/showers are the result of an approaching cold front. Ongoing line of deep convection over the TN valley is forecast to weaken this morning before redeveloping along the outflow boundary as it moves into the western Appalachians this afternoon. Storm coverage the afternoon is expected to be scattered in nature...thunderstorm clusters as opposed to a solid line. Southerly winds will become a bit gusty from mid morning on per 35 to 40 knot LLJ ahead of the approaching front. Showers/Storms are forecast to linger until loss of daytime heating. The actual surface front is expected to wash out and dissipate as it crosses the mountains, so in spite of a wind shift as it crosses the mountains this evening, very little if any wind shift is expected over the piedmont east of the mountains where the winds will remain predominantly out of the south or southwest. Extended Aviation Discussion... Mainly VFR flying weather is expected for Friday and into the weekend as high pressure builds over the southeast states promoting temperatures which will be much above normal. Warming surface temperatures also means increasing atmospheric instability. As such, potential will exist for cloud build-ups and the risk for isolated to scattered thunderstorms along the spine of the Appalachians during the peak heating hours each afternoon. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PW NEAR TERM...PM/PW SHORT TERM...PC LONG TERM...KK AVIATION...PM

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