Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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566 FXUS62 KRAH 260800 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 400 AM EDT FRI AUG 26 2016 .SYNOPSIS... A strong upper level ridge will extend across the region through the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 345 AM Friday... A strong 595dm ridge at 500mb will shift overhead today, while a 850mb thermal ridge characterized by temps around 20C sets up from the TN Valley to central VA. 1000-850mb thicknesses are expected to start out around 1420m this morning, 15m higher than Friday, which supports the warmer MET guidance and highs in the mid to maybe even some upper 90s. Dewpoints in the lower 70s will push heat indices back toward 105 in the coastal plain. Forcing for convection is generally non- existent, but a few storms may strong within a ribbon of moisture, noted on water vapor, shifting from the blue ridge toward the southern Piedmont. Any convection would be very isolated and barely warrants any mention in the forecast. The upper ridge will continue its migration toward the northeast tonight, while a weak surface trough slips into the area form the north and winds begin to turn to northeasterly late. Lows 70-73 && .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... As of 345 AM Friday... With the upper ridge to our north on Saturday, northeasterly flow will set in, though with very little change in airmass and highs again in the mid 90s. A slight dip in 850mb temps and reduction of the mid-level cap should allow isolated to widely scattered convection to fire during the afternoon, mainly with an axis of weak to moderate instability across the southern Piedmont and coastal plain. Convection will be diurnally driven and dissipate by early evening, with northeasterly flow supporting a chance of some low clouds over the coastal plain by early Sunday morning. Lows 70-73. && .LONG TERM /SUNDAY THROUGH THURSDAY/...
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AS OF 355 AM Friday... Above average forecast uncertainty remains today thanks to the still unknown, if at all, development and subsequent track of the tropical wave located between the SERN Bahamas and Cuba. This system remains poorly organized this morning; and the probability of subsequent development into a tropical cyclone appears lower than previous days. The wave will nonetheless bear watching and remain the primary forecast concern for much of the SERN and Gulf coast states, including central NC, as it drifts WNWWD during the next few days. A mid to upper low developing now several hundred miles W of Bermuda will drift W --around the SRN periphery of an initially strong sub- tropical ridge forecast to migrate across the Central Appalachians and Middle Atlantic states-- and consequently approach the SE U.S. coast late Sun-Mon. The approach of this low will provide synoptic- scale forcing for ascent atop a zone of low level convergence over the ERN Carolinas, in association with both the sea breeze and frictional convergence in moist ENE low level flow around surface high pressure initially along the Middle Atlantic coast. The presence of the surface ridge axis extending SWWD across the interior Middle Atlantic states will cause surface dewpoints to mix out well into the 60s Sun-Mon, while a much more humid air mass will envelop coastal areas and the coastal plain. The forecast will consequently be a dry one for the Piedmont, while diurnal convection will be possible generally along and east of I-95 each afternoon. The presence of the mid-upper low and associated height falls will also cause the sub-tropical ridge to split, with an associated positively-tilted trough/shear axis invof the SERN and SRN Middle Atlantic coasts early to mid week. This weakness in the ridge will provide a corridor through which low pressure associated with the aforementioned tropical wave could pass, though if the wave were to indeed remain weak/shallow, it would more likely continue a WNW drift across the GOM. Given continued large model spread, and doubt about any appreciable development of the tropical wave at all, only minimal changes have been made to the previous forecasts for mid-week.
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&& .AVIATION /08Z FRIDAY THROUGH TUESDAY/... As of 200 AM Friday... Strong high pressure over the region will lead to light/variable predominately VFR conditions today an tonight, with just some scattered clouds above 4k ft drifting east across the Piedmont this morning. A chance for some isolated pockets of MVFR vsbys also continue this morning, particularly after 09z at FAY AND RWI. Outlook: This area of high pressure is expected to maintain its influence over our region through early next week. A weak backdoor cold front early Saturday will be followed by a northeast wind that could lead to some sub-VFR ceilings across the coastal plain on Sunday morning. Otherwise, VFR conditions are expected to prevail. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...BS NEAR TERM...BS SHORT TERM...BS LONG TERM...MWS AVIATION...BS

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