Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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186 FXUS62 KRAH 251058 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 655 AM 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 350 AM Wednesday... height rises (90m at KGSO last evening) continue across much of the eastern US, while a surface high has become established off the Southeast coast. Moisture recovery is underway but will be slow with dewpoints only in the upper 50s today. A modest subsidence inversion noted on the 00Z/25th KGSO RAOB and weak instability will inhibit any convection today. There is a weak disturbance upstream that will drift over western NC and may weaken the cap a bit, but hi- res WRF/HRRR guidance keeps all convection over or west of the mountains today. H10-H85 thicknesses starting out about 15m higher than Tuesday morning suggest highs about 5 degrees warmer, 84-89. 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. && .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 /12Z Wednesday through Sunday/...
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As of 645 AM Wednesday... As high pressure expands over the Southeast US, VFR conditions will prevail through the current TAF period with a light southwesterly wind. Showers and storms remain over or west of the mountains today, with just some increase in mid-clouds from the west late tonight. Outlook: VFR conditions will prevail across central NC through Friday. Meanwhile, the chance afternoon showers and storms will increase, mainly across western NC, with adverse aviation much more likely by Sunday as a low pressure system develops off the Southeast coast.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...BLS NEAR TERM...BLS SHORT TERM...BLS LONG TERM...26 AVIATION...BLS

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