Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 160621 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 220 AM EDT Wed Aug 16 2017 .SYNOPSIS... A weak area of low pressure and a surface trough will linger near and off the Carolina coast through Wednesday night. A slightly drier air mass will move into the region on Wednesday. A back door cold front will drop into the region on Thursday and Friday before another cold front approaches from the northwest on Saturday. && .NEAR TERM /TODAY THROUGH TONIGHT/... As of 205 AM Wednesday... Pretty quiet day expected. Last evening`s convection has culminated in a weak surface trough extending from coastal NC SW and W across northern SC, setting up a low level flow from the N over much of central NC today. The dry/stable trajectory is evident up through 850 mb on the 00z upper air analyses, with NW flow at GSO and troughing over the eastern Carolinas, and warm/subsident mid levels. 850 mb progs show the trough just aloft settling to our south with flow veering to northerly in eastern NC as a weak mesohigh forms over the NC Foothills and western Piedmont today. We`ll likely see stratus and patches of fog this morning, thickest and most widespread across the northeast CWA beneath a focused 10-15 kts 925 mb jetlet from the NE, although this feature will weaken and dissipate by afternoon, allowing for dispersion of the low clouds and a trend toward more sunshine. Expect partly to mostly sunny skies this afternoon, with minimal convection chances late in the day confined to the far S and W CWA where PW values should hold close to 2.0", while dipping to near 1.5" or lower elsewhere. Highs 87-92 with slightly above normal thicknesses countering the morning clouds and delayed insolation. Expect dry weather this evening and tonight, although we`ll need to watch for eastward drift of scattered convection off the higher terrain into the NW CWA overnight. Lows 71-76 under fair to partly cloudy skies. -GIH && .SHORT TERM /Thursday and Thursday night/...
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As of 220 AM Wednesday... Brief mid level shortwave ridging early Thu over the Southeast will give way to falling heights aloft and a WSW steering flow by Thu night, as potent northern stream shortwave troughing crosses the upper Midwest. Today`s weak boundary to our south will be all but gone by Thu, leaving just a weak surface trough from western NC down through SC, and a light surface flow from the SE and S over NC. A subtle low-mid level warm frontal zone, seen on last evening`s 700 mb analysis extending from Nebraska through the MO Bootheel to MS and southern AL, will steadily progress to the NE and E, shifting across the interior Mid Atlantic and NC Thu morning through Thu evening. The presence of this deeper moisture, weak forcing for ascent, and daytime heating should prompt scattered showers and storms, spreading eastward through the day. Coverage should be slightly better across the NW CWA, closer to the lower mid level heights, as compared to the S/E CWA. Under partly to mostly cloudy skies, expect highs of 89-93 as thicknesses stay above normal. Pops should decrease in the evening with loss of heating and passage of the mid level moisture ridge to our east, but with such high surface dewpoints anticipated and the possibility of weak boundaries meandering about, will leave in a slight chance overnight. Lows in the mid 70s. -GIH
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&& .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 239 PM Tuesday... Thursday and Friday...the risk for scattered showers/tstms remains in the forecast as a series of weak short waves move across in the wsw flow aloft. A more robust short wave trough is progged to approach on Saturday and lift by to our north on Sunday, and pushing a cold front down into the Carolinas in the process, and providing the synoptic scale support for additional rounds of scattered showers/tstms both Saturday and Sunday. With the upper trough pulling away and zonal or broad cyclonic flow left in its wake, the sfc boundary and moisture pool gets left behind across the Carolinas for early next week, thus continuing the daily risk for showers/tstms Monday and perhaps Tuesday, and also elevating the risk for the presence of clouds during the eclipse. Temps will run at or above normal through the period with no significant airmass changes. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... As of 1230 AM Wednesday... Earlier showers/storms have exited central NC, leaving beyond VFR conditions but plenty of low level moisture both in the area and upstream. Weak low pressure over eastern NC and a trailing trough extending back along the NC/SC border will become more defined today, with low level flow becoming uniformly from the NNE/NE. Latest high resolution models show widespread IFR/LIFR stratus and MVFR/IFR fog drifting southward from VA and expanding, impacting central NC TAF sites between 07z and 16z this morning. RDU/RWI is likely to see the longest period of sub-VFR conditions early this morning, but such conditions are expected for at least a few hours at all sites. After about 16z, the low clouds will break up and lift, bringing VFR conditions to all sites, lasting through the end of the TAF valid period, with a couple of exceptions: First, there is a chance of a shower or storm, mainly in the SE (FAY), from around 19z to around 02z, which may bring a period of sub-VFR conditions and erratic winds. And, IFR conditions are likely to develop at RWI starting near the end of the forecast period, after 05z. Winds will be light (under 8 kts) from the NNE or NE today, becoming variable under 4 kts this evening through tonight. Looking beyond 06z Thu, IFR conditions are likely overnight into Thu morning in the NE (RWI), with just MVFR fog possible elsewhere. There is a good chance for showers and isolated storms both Thu and Fri afternoon, and sub-VFR fog/stratus are expected late Thu night into Fri morning and again late Fri night/Sat morning. Mainly afternoon and evening showers and storms are possible Sat through Sun as a cold front approaches from the NW. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...JB NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...np AVIATION...Hartfield

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