Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 271827 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 227 PM EDT Thu Apr 27 2017 .SYNOPSIS... 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. && .NEAR TERM /THROUGH TONIGHT/... As of 1155 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. The latest high resolution models show scattered showers and thunderstorms developing over the Tennessee River Valley and spreading eastward toward locations west of the Blue Ridge, but the timing has slowed down by a couple hours and is reflected in this latest update. 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. && .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 /18Z THURSDAY THROUGH TUESDAY/...
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As of 225 PM EDT Thursday... VFR conditions should persist for most locations this afternoon, but there will be scattered showers and thunderstorms that could limit ceilings and visibilities to MVFR temporarily. An old outflow boundary ahead of an approaching cold front in the Ohio River Valley will reach the western Appalachian Mountains, which should serve as the focal point for any convection. The best confidence for timing of the showers and thunderstorms comes between 20Z Thursday to 02Z Friday. Winds will gust out of the southwest this afternoon due to a 40 knot low level jet. By tonight, shower and thunderstorm activity should dissipate as the outflow boundary exits to the east. Model guidance shows ceilings dropping toward MVFR and possibly even lower at BLF/LWB/BCB during the night, but confidence was too low at this time to push it downward as much. Patchy fog will also be possible at LWB and BCB by early Friday morning, while locations in the Piedmont should remain VFR. All TAF sites should return to VFR after 12Z Friday with light south winds expected. Extended Aviation Discussion... High pressure should build off the Southeast coast during this weekend. Other than the potential for MVFR/IFR morning fog at the usual river valley locations, VFR conditions should prevail through Saturday. As a low pressure system approaches from the west on Sunday and Monday, the potential for afternoon showers and thunderstorms will increase. The cold front associated with this system should reach the Appalachian Mountains by Monday afternoon and depart offshore on Tuesday morning, so expect the best chance of MVFR conditions during the frontal passage.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PW NEAR TERM...PM/PW SHORT TERM...PC LONG TERM...KK AVIATION...PW

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