Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 170744 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 345 AM EDT Thu Aug 17 2017 .SYNOPSIS... A surface low pressure trough will extend from western North Carolina through South Carolina today through tonight. This trough will shift northeastward late tonight, and then hold over the Piedmont Friday through Saturday. && .NEAR TERM /Today through tonight/...
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As of 320 AM Thursday... The weak mid level wave noted on water vapor imagery over central and eastern NC will move off the coast this morning, leaving brief mid level shortwave ridging in its wake. Today`s surface pattern will feature a weak low over SC, with a trough extending to its east and northward through the NC Foothills and far W Piedmont. Weak surface high pressure over NE NC and E VA/Delmarva will weaken today as the W NC trough becomes better defined, with southerly flow developing over central NC. Both surface dewpoints and PW will be on the rise today, corresponding to W-to-E passage of a diffuse moisture band at 700 mb. While the deep layer wind field remains rather weak with only minor to absent dynamic forcing for ascent, the warm low levels and deepening moisture should be enough to instigate scattered to numerous showers and storms today, developing first through the heart of the Piedmont before easing eastward into the Coastal Plain later in the day. The GFS projects peak late-day MUCAPE of 1500-2500 J/kg, but with deep layer shear under 20 kts, suggesting a low risk of organized severe storms, although isolated strong pulse wind-producing storms are possible mid afternoon through early evening. Isolated showers and storms will remain possible overnight within lingering elevated instability as the 950- 900 mb layer remains quite warm with plentiful low level moisture, especially in the east, along and east what the Piedmont trough. Mid level lapse rates should also remain elevated, above 6 C/km, overnight. Highs 89-94 today, and the high dewpoints will push heat indices to 100-103 over the Sandhills. Warm and muggy lows tonight of 72-76 under partly cloudy skies with patchy fog. -GIH
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&& .SHORT TERM /Friday through Friday night/...
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As of 345 AM Thursday... Weak mid level height falls will continue into Fri as a shortwave trough pivots from Michigan/SE Ontario through the St Lawrence Valley, with a weaker/broad reflection down through the southern Appalachians. The Piedmont trough will strengthen and shift slightly eastward through Fri night, with plentiful low level moisture remaining in place over central NC (especially along and east of the surface trough), PW over 2.0", and passage of weak perturbations within the gently cyclonic southwesterly mid level flow. Under these conditions, convection should start early, in the morning (as soon as the surface-based inversion mixes out), over the Coastal Plain and eastern Piedmont/Sandhills. Additional convection is likely by afternoon just to our W and NW, over the Appalachians, and this should slide eastward later in the day, bringing a second peak in shower and storm coverage over central NC during the evening and early overnight hours. Expect plenty of clouds near and soon after daybreak, perhaps briefly breaking up with mixing, mainly over the southwest, before broken to overcast skies redevelop quickly with heating. Highs 89-95 with partly to mostly cloudy skies. Expect a good chance of showers/storms in the evening, decreasing and shifting southeast overnight as the surface trough kicks east toward the coast with a weak surface high building into W NC from the west. Lows from 70 NW to 76 SE. -GIH
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&& .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 335 AM Thursday... A strong low pressure system moving north of the Great Lakes will move eastward and drag a cold front across the Carolinas on Friday and Friday night before stalling out near the Carolina Coast. This will keep precip chances in the forecast for Friday and but should confine things to the extreme southeastern portions of the area by Friday night. With the leftovers hanging around for much of the weekend expect eastern areas to maintain higher precip chances through much of the weekend. As the weekend comes to a close, continental high pressure will move in from the northwest which could help to lower precip chances by Sunday afternoon/evening. Interesting forecast for the eclipse on Monday with models starting to come into agreement with zonal flow aloft and surface high pressure sitting right off of the Carolina Coast. The positioning of the high pressure will most likely yield moist return flow around the back side of the high which unfortunately would most likely lead to at least partial cloud cover for Monday afternoon. That being said, the GFS solution is interesting that it lags the continental high back to the west a little bit and if that happens it could potentially suppress cloud cover to the south. Still way too early tell but at least a partly cloudy forecast looks likely. For midweek return flow around the high will continue, bringing daily precip chances with another surface low well to the north that may bring another front through the area by later on Wednesday. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... As of 125 AM Thursday... An area of IFR conditions is expected early this morning over northeast portions of central NC, including RWI, where vsbys have already dropped to MVFR in fog. Confidence is high that RWI will see mainly IFR conditions developing, peaking 08z-12z this morning. RDU and FAY will see a lower threat of IFR conditions, although MVFR fog is still possible at these two sites. INT/GSO will see only a slight chance of sub-VFR conditions this morning. After 13z, cigs/vsbys at RWI are expected to improve to VFR by 15z. VFR conditions will then dominate through the day, although scattered showers and storms generating a period of sub-VFR conditions and erratic winds will be possible at each site, mainly 18z-00z. VFR conditions should prevail this evening into tonight, although MVFR fog may develop starting around 05z. Winds will be light and variable this morning, becoming mostly from the south by midday, at 6-10 kts this afternoon diminishing to 3-6 kts starting this evening. Looking beyond 06z Fri, good chance of MVFR fog at all sites 06z- 12z, followed by VFR conditions after 13z. Scattered showers and storms are possible mainly mid afternoon through mid evening Fri, although additional isolated storms remain possible through Fri night, with a chance for sub-VFR fog/stratus. Best shower/storm chances shift to our SE for Sat into Mon, with VFR conditions prevailing, although FAY may continue to see a storm threat. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...Ellis AVIATION...Hartfield

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