Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 121144 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 644 AM EST Thu Jan 12 2017 .SYNOPSIS... High pressure over the western Atlantic will extend westward across the area through early Friday. A backdoor cold front will enter the state from the north late Friday, and push through the area to our south Friday night. && .NEAR TERM /THROUGH TONIGHT/... AS OF 340 AM Thursday... Fog has been slow to develop this morning but is finally setting in over the northwest Piedmont in the pronounced but apparently eroding wedge airmass. RAP and NAM soundings suggest the fog will hold through 8 or 9am, but BUY and EXX recently saw some visibility improvement, so the fog may indeed abate a little sooner. Increased dewpoints behind the front should resulting some scattered cu today, with otherwise clearing of high clouds and good insolation. Combined with broad southerly flow between the high offshore and the nearly stalled frontal zone west of the mountains, highs should have little trouble reaching the upper 60s and lower 70s. The one exception may be the Triad area where early low clouds and lingering snow melt may inhibit heating slightly. Forecasting a range of 63-72 northwest to southeast. May also see some wind gusts to around 20kt by this afternoon. The aforementioned front will hold to our northwest and begin to lay west to east across VA as the subtropical ridge builds over the Southeast. Moist southerly flow will again promote the development of stratus and/or fog, with less in the way of high clouds and a weakening SLP gradient possibly favoring some fog late, especially across the northern Piedmont/Coastal Plain. Lows 48-53. && .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... AS OF 340 AM Thursday... The passage of a shortwave over the Great Lakes will weaken the northern periphery of the upper ridge on Friday, with the cold front to our north aided south into the area late Friday afternoon and evening by an arctic high shifting east over New England. Timing of the front will influence high temps, with guidance currently indicating it reaching the northern Piedmont at or after peaking heating. An increasing in clouds (mainly high at first) may hold back heating in the north as well, but it seems reasonable for temps to reach the mid 60s north to lower 70s southwest, a general consensus of statistical guidance. This type of pattern typically features a side range from north to south. The cold front will surge through the area Friday night, accompanied by 10-15kt winds and the obvious drop in temps. 1000-850mb thicknesses remain above 1310m and forecast soundings suggest wetbulb temps will remain just above freezing, such that the light qpf that models generate from weak 285-290K isentropic/upslope ascent should not result in any freezing rain. expect lows in the mid 30s north to mid 40s south. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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As of 355 AM Thursday... The mid latitudes, including the Srn Middle Atlantic states, will be a battleground between 1) a subtropical ridge over the SErn U.S., 2) a srn stream trough over the SWrn U.S., and 3) a broad nrn stream trough over Ern Canada. Confluent flow between the three, over the NErn quarter of the U.S., will support the Ewd migration and maintenance of arctic surface high pressure --a series of them-- from the Nrn Plains to the NErn U.S. Episodes of resultant damming E of the Appalachians and into the Srn Middle Atlantic (VA/NC) will result through early next week. CAD --and associated cool and cloudy conditions in the 40s to lower 50s-- will be maximized both Sat and Mon. The subtropical ridge will become increasingly amplified/dominant Tue-Wed, supportive of a warming and more humid southwesterly flow. After a chance of drizzle or light rain during the episodes of CAD through early week, the best chance of any appreciable precipitation --in the form of rain showers-- will be with the approach and eventual passage of a slow-moving cold front mid to late week.
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&& .AVIATION /12Z THURSDAY THROUGH MONDAY/...
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AS OF 644 AM Thursday... Moist southerly flow has resulted in a warm front moving north through almost all of the area, with a wedge-like airmass and IFR conditions currently hanging on at INT. The RAP suggests IFR conditions will hold for a couple more hours at INT and then improve by 14Z, while GSO should remain predominately VFR. All other sites (RDU/FAY/RWI) are expected to remain VFR today, with a 10-14kt southerly wind that will gust to 20-25kt. With less high clouds tonight and a light southerly wind, the potential will again exist for some low clouds and fog. Confidence is below average at this point, but the pattern would favor mostly IFR or MVFR conditions. Long term: VFR is expected early Friday before a cold front moves in from the north and brings the potential for a prolonged period of low clouds for the upcoming.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...HARTFIELD NEAR TERM...SMITH SHORT TERM...SMITH LONG TERM...MWS AVIATION...SMITH

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