Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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209 FXUS62 KRAH 261652 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1255 PM EDT FRI AUG 26 2016 .SYNOPSIS... An upper level ridge will extend across the region through the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 1220 PM Friday... Have issued a heat advisory for locations generally along and east of highway 1 through 7 PM this evening. Afternoon temps in the upper 90s appear likely and with dewpoints in the lower 70s, heat index values will likely reach the critical threshold of 105. Weak sfc trough extending from the coastal plain through the sandhills and southern piedmont will aid to pool low level moisture. May see enough lift occur along the boundary to initiate an isolated shower or storm, most probable over parts of the sandhills and southern piedmont. Still, isolated nature of the convection means that most folks will not get any relief from the intense afternoon heat. Tonight, expect clear to partly cloudy skies and it will feel muggy as sfc dewpoints recover into the lower 70s. Overnight temps in the low-mid 70s. && .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/... 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. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... As of 1255 PM Friday... There is high confidence that VFR conditions will persist across central NC through Saturday night. The exception will be a threat for isolated convection Saturday afternoon and associated MVFR conditions/gusty sfc winds. Otherwise, an area of high pressure will maintain dry weather with light wind conditions. This area of high pressure is expected to maintain its influence over our region through early next week. Circulation around the sfc high may advect enough low level moisture to result in a period of stratus Sunday morning and again Monday morning. Also, there will be a threat for isolated afternoon/early evening convection Sunday through Wednesday mainly in the vicinity of KFAY (associated with the seabreeze), and the Triad terminals (convection drifting off the higher terrain into the western Piedmont). && .RAH WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 7 PM EDT this evening for NCZ010-011- 026>028-041>043-075>078-084>086-088-089. && $$ SYNOPSIS...BS NEAR TERM...WSS SHORT TERM...BS LONG TERM...MWS AVIATION...WSS

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