Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 212003 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 403 PM EDT Mon Aug 21 2017 .SYNOPSIS... A decaying stationary front extending across northern South Carolina into Georgia will dissipate tonight. Weak surface high pressure near the Mid-Atlantic coast will move offshore tonight and Tuesday as a lee trough develops in the Piedmont of Virginia and the Carolinas. A strong cold front will across the area on Wednesday and reach the coast on Thursday. && .NEAR TERM /THROUGH TONIGHT/... As of 345 PM Monday... Latest surface analysis shows a decaying stationary front extending from coastal SC west into GA with weak surface high pressure off the Mid-Atlantic coast. A light east to southeast flow has developed at the surface and 925 hPa across central NC which contributed to an upward surge in dew points this morning before afternoon mixing knocked them back into the upper 60s to lower 70s. A shear axis/convergence zone across the western Piedmont resulted in the development of a few rogue storms across the Triad early this afternoon (unfortunately around eclipse time) with other scattered storms developing in convergence across the higher terrain. Mainly clear skies with no precipitation is noted across the remainder of the RAH CWA. The threat of isolated convection will persist through most of the afternoon across the Triad and western Piedmont in a region of weak to moderate instability (MLCAPE values around 1000-1800 J/kg) and modest mid level lapse rates. An even more limited threat of convection will continue across the far southern Coastal Plain for the next few hours in southern Wayne, Sampson and Cumberland Counties. Any convection should quickly dissipate by around sunset. Mainly clear skies this evening will give way to increasing low clouds and fog across the Coastal Plain and Sandhills late tonight toward daybreak. Fair weather with mostly clear skies are expected across most of the Piedmont. Overnight lows will range between 71 and 75 degrees. -Blaes && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... As of 230 AM Monday... Heights aloft fall slightly on Tuesday with the approach of the northern stream trough and attendant cold front into the Ohio and Tn Valleys late Tuesday/Tuesday night. While we do see the development of pre-frontal sfc trough in the lee of the mountains Tuesday afternoon, central NC remains in a void of appreciable synoptic scale lift. And as such, convective rain chances should remain rather low and generally confined across the far SE zones in the vicinity of the sea breeze and across the western part of the state along the pre-frontal trough. One minor caveat that needs to be mentioned is a sheared vorticity centered that`s currently off the SE coast. If this feature can hold together as it moves westward over the SE states, where it will encounter the upper level anticyclone, DPVA from this feature could serve to support slightly higher/better rain chances across the southern zones. Will continue monitor will only slight chance pops for now. Loss of daytime heating should Tuesday evening should lead to dry conditions overnight as the cold front doesn`t`t arrive from the NW until late Wednesday afternoon. Highs in the lower 90s with lows in the lower to mid 70s. && .LONG TERM /WEDNESDAY THROUGH MONDAY/...
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As of 400 PM Monday... A high chance to likely probability of showers and storms late Wed- Wed night will linger over the sern half of the CWFA on Thu, followed by mainly dry conditions and temperatures near to about 5 degrees below average Fri-Mon. The models are in relatively good agreement that a lead mid level trough/shear axis, including some localized vorticity maxima likely related to earlier upstream convection, will be draped at 12Z Wed from the New England coast swwd across the central Appalachians and Mid-South. This feature and associated forcing for ascent will drift across central NC Wed and early Wed night and then reach the coast by Thu morning. A related surface cold front will overtake a preceding Appalachian-lee trough early Wed, then drift slowly sewd into central NC late Wed afternoon and Wed evening, before settling through sern NC on Thu. A trailing mid-upper level trough axis and upper jet right entrance region will pivot across the Middle Atlantic states on Thu, followed by lingering broad troughing aloft, and underlying surface ridging, over the ern US through the end of the period. Weak to moderate warm-sector instability on Wed, fueled by early day sun and temperatures in the upper 80s to lower to perhaps middle 90s, and ~25 kts of mid level wly flow, will likely support a few generally ewd-propagating clusters capable of producing strong- severe wind gusts Wed aft-eve. There may be a lull in precipitation after midnight, when guidance indicates a relative minimum in deep layer omega, and when diabatic cooling will have reduced instability. However, the approach of the trailing mid-upper trough axis/jet, in conjunction with lingering frontal forcing over sern NC, should result in convective redevelopment in the vicinity of the front from the srn piedmont and Sandhills to the ern piedmont and Coastal Plain. It will otherwise be cloudy early, becoming partly to mostly sunny, with high temperatures in the upper 70s to middle 80s. Cool weather will continue through the weekend owing to the presence of the surface ridge axis and associated nely low level flow.
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&& .AVIATION /18Z MONDAY THROUGH FRIDAY/... As of 225 PM Monday... Widespread VFR conditions are expected through the afternoon evening hours across central NC with the exception of some isolated storms in the Triad terminals (KINT and KGSO) and perhaps near but especially southeast of the KFAY terminal. Elsewhere scattered cumulus with bases around 4kft are expected. Convection will dissipate this evening with mainly clear skies developing for the evening and early overnight hours. Another round of late night and early morning fog and stratus is expected to develop across the Coastal Plain and Sandhills region with IFR to MVFR conditions at the KRWI and KFAY terminals. Restrictions will improve by mid morning Tuesday. Looking beyond the 24 hour TAF period...isolated to scattered afternoon and evening showers and storms are expected on Tuesday. A cold front will move across the area on Wednesday providing a much greater chance of showers and storms areawide with the front moving toward the coast on Thursday on Thursday. High pressure building in behind the front will result in fair weather for friday into the weekend. -Blaes && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Blaes NEAR TERM...Blaes SHORT TERM...CBL LONG TERM...MWS AVIATION...Blaes is the U.S. government's official web portal to all federal, state and local government web resources and services.