Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 161046 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 645 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/... 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 && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... As of 300 AM Wednesday... Friday and Friday night: An upper level shortwave trough and surface cold front will approach the region from the west on Friday, though it will likely get hung up over the mountains. As a result, strong southwesterly flow over Central NC will result in warm, humid conditions and the best chances for convection will be along differential heating boundaries near the foothills and along the sea breeze. For now, Friday night appears to be largely dry, although if enough pre-frontal moisture makes its way into Central NC, some convection could persist into the night. Highs in the upper 80s to mid 90s and lows in the low to mid 70s expected. Saturday and Sunday: A stronger upper level trough and surface cold front will approach from the west on Saturday, with the upper level trough swinging through the region and deamplifying as it does so Saturday night into Sunday. Although the front appears quite strong, it is expected to stall over Central NC, having a hard time progressing through the area before getting washed out Sunday night. Best chances for convection will be in proximity to the stalled front, lower in its wake, Saturday and Saturday night. Chances for convection could decrease further on Sunday, again with the highest chances farther southeast. Southerly to southwesterly flow at the surface will be enhanced ahead of the front with return flow around the Bermuda High extending into the region. Highs will generally remain in the upper 80s to low 90s over the weekend (although if the front progresses into the region a bit further it will affect temps to the northwest). Lows generally in the low to mid 70s. Monday onward: Surface high pressure will build off the Mid-Atlantic coast, with continued southerly flow over Central NC through mid- week. Aloft, high pressure will build over the Southeast U.S. with a trough amplifying over the Midwest Tuesday and progressing east- southeastward. With the little change in airmass expected, continued diurnal convection in the favored areas will be most likely. As for temperatures, expect highs generally in the mid 80s North to low 90s South and lows in the upper 60s to mid 70s. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
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As of 645 AM Wednesday... High probability of dominant IFR/LIFR conditions at RWI/RDU for the next few hours, with lower confidence and less coverage (if it occurs at all) at INT/GSO/FAY. A weak low pressure trough extending from eastern NC SW and W along the NC/SC border will become more defined today, with low level flow becoming uniformly from the NNE/NE. Latest high resolution models continue to support IFR/LIFR conditions over SE VA drifting to the ESE over northeast sections of central NC through 13z, followed by improvement to VFR by 15z or 16z. RDU/RWI is likely to see the longest period of sub-VFR conditions early this morning. After 15z-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: There is a slight chance of a shower or storm, mainly impacting INT or 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 in the last hours of the forecast period, after 06z. Winds will be light (under 8 kts) from the NNE or NE today, becoming variable under 4 kts this evening through tonight. Looking beyond 12z Thu, IFR conditions are likely to hold 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
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...JB NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...KC AVIATION...Hartfield

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