Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 161455 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1050 AM EDT Wed Aug 16 2017 .SYNOPSIS... A surface trough will extend along the North Carolina coast southwestward into central South Carolina and Georgia through Thursday. A back door cold front will approach the region on Thursday before another cold front approaches from the northwest on Friday and moves into the region on Saturday. && .NEAR TERM /TODAY THROUGH TONIGHT/... As of 1050 AM Wednesday... The latest surface analysis shows a surface trough extending northeast to southwest along the NC coast and then laying across central SC and GA. A cold front extended from the northern Chesapeake Bay westward to the Ohio river valley. The air mass across central NC was still very moist with surface dew points in the lower to mid 70s in most locations but exceptionally nasty at KMEB (TD 80) and KGSO (TD 81) at 10am. Morning fog an stratus had eroded a bit with a small region of overcast across the central Coastal Plain. Elsewhere, scattered cumulus was beginning to develop with surface heating. Convective coverage should be more limited this afternoon and evening than previous days and the upcoming period as forcing for ascent is limited across central NC. In addition, slightly drier and more stable air will move into north-central NC this afternoon. Low level convergence in proximity to the surface trough will support isolated to scattered storms this afternoon and early evening in an arc from the coastal region of NC westward across the Sandhills into the western Piedmont. Little if any convection is expected from Raleigh northeast. Low-level thickness values this morning are similar to yesterday`s and support highs between 88 and 94 with lows tonight in the lower to mid 70s. -Blaes && .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/... 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 && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Blaes NEAR TERM...Blaes SHORT TERM...Hartfield LONG TERM...KC AVIATION...Hartfield

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