Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 251710 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 110 PM EDT Wed May 25 2016 .SYNOPSIS...Surface high pressure will extend into the region through Friday. Meanwhile, a storm system will develop over the sub-tropical Atlantic and drift toward the Southeast coast through the weekend. && .NEAR TERM /through tonight/... As of 1045 AM Wednesday... Little change/adjusted required to the near term forecast. Anti-cyclonic flow, a result of a mid/upper level ridge over the Deep South and TN Valley, will maintain warm and dry conditions today across central NC. While the lower layers of the atmosphere will become slightly unstable this afternoon, a subsidence inversion between 750-650mb will act as a cap, inhibiting convective development. Low level thicknesses this afternoon projected to reach the 1410- 1415m range, a solid 15m warmer than normal. This suggest max temps in the mid-upper 80s, in line with current forecast. -WSS Conditions will again be good for radiational cooling tonight, the exception being the western Piedmont where patchy mid/high clouds associated with upstream convection may become mostly cloudy for a period late in the night. Lows in the upper 50s and lower 60s. -BLS && .SHORT TERM /Thursday through Thursday Night/... As of 350 AM Wednesday... While high pressure, both at the surface and aloft, will remain over the region on Thursday, increasing PW to near 1.5" and a little better instability (500-1000 J/KG) will support a better chance of convection, mainly in the western Piedmont from storms moving off the higher terrain. The environment won`t be supportive of organized convection, so the threat of any strong storms is low and will be limited to enhancement from steepening low-level lapse rates. highs again in the upper 80s. The GFS appears much too aggressive with convection continuing into Thursday night given that the ridge will begin to restrengthen in response to the subtropical system developing over the northern Caribbean. Instead, skies should end up mostly clear and lows will dip back into the low/mid 60s. && .LONG TERM /Friday through Tuesday/... As of 405 AM Wednesday... Little change in the overall forecast rationale...driven by a pattern aloft characterized by a western CONUS trough and a ridge from near Bermuda to central Canada. A southern stream mid to upper- level low will meanwhile develop/evolve in the vicinity of the Bahamas, at the base of/beneath the eastern ridge. Model guidance now unanimously support some degree of low pressure development over the western Atlantic Ocean/east of the Bahamas, along an old, weakening frontal zone. This low may acquire sub- tropical or tropical characteristics as it is steered WNW toward the southeast U.S. coast, between the aforementioned low/ridge couplet, though model spread with the eventual track of the low is large. Regardless, it still appears Fri into the first part of Saturday should remain under the influence of ridging at the surface and aloft, with mid-upper 80s warmth on Fri remaining comfortable owing to surface dewpoints in the upper 50s to lower 60s. This relatively dry BL, in conjunction with a capping inversion aloft, should maintain generally dry conditions throughout central NC. Later Sat-Tue: A deep feed of SE flow between the low/ridge couplet will promote increasing clouds/deep moisture, with precipitable water values forecast to climb to between 1-2 standard deviations above normal. While this increase in moisture will prime the environment for above average chances of showers and storms, the ultimate track of the aforementioned low will play a role in rainfall coverage and amounts (I.E. an enhancement if the low were to move into the Carolinas, or conversely a reduction if the low were to remain offshore and promote peripheral subsidence of the otherwise moist air mass). Given the large model spread, will largely defer to the WPC fronts/pressure and forecast elements, which takes the low into the Savannah Basin early next week, with PoP maximized diurnally in the 40-50 % range Sun-Tue. Temperatures, tempered by clouds and convection, should be near normal, albeit with high humidity owing to the mT air mass that will have infiltrated at least the central and eastern Carolinas. && .AVIATION /18Z Wednesday through Memorial Day/...
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As of 110 PM Wednesday... An area of high pressure at the surface and aloft will maintain VFR conditions across central NC through Thursday night. The exception will be a slight threat for isolated afternoon-early evening convection on Thursday, mainly over the western Piedmont. Where the isolated convection occurs, expect MVFR ceilings and visibility as well as gusty sfc winds. Aviation conditions varying between VFR and MVFR will occur Friday and Saturday, mainly due to early morning fog and/or low stratus, and isolated-scattered afternoon through early evening convection. The probability for adverse aviation conditions will increase Sunday and Memorial Day as an area of low pressure off the southeast U.S. coast spreads deep moisture into our region resulting in sub_VFR ceilings and an increasing threat for scattered convection.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...BLS NEAR TERM...WSS/BLS SHORT TERM...BLS LONG TERM...26 AVIATION...WSS is the U.S. government's official web portal to all federal, state and local government web resources and services.