Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 200620 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 215 AM EDT Thu Apr 20 2017 .SYNOPSIS...
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A cool wedge of high pressure extending into the Carolinas early today will give way to a surge of warmer air this afternoon. A cold front will approach from the northwest late Friday, then stall over North Carolina on Saturday. A strong storm system will move across the Carolinas on Sunday.
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&& .NEAR TERM /THROUGH TONIGHT/... As of 1025 PM Thursday... The strong surface high to the north will continue to lift off to the north and east tonight. However, a lingering CAD air mass remains over the Piedmont of central NC this evening, with the most notable presence across the NW Piedmont where low stratus and temps in the upper 50s still rule. While the CAD has generally weakened this evening with the CAD boundary slowly retreating north and westward, we still expect it to linger over at least the NW Piedmont tonight, with renewed low stratus and/or fog developing after midnight in areas that have cleared out some. However, the main concern overnight is the potential for areas of fog (some possibly dense), primarily in the lingering CAD wedge over the NW Piedmont, where the HRRR has shown the potential for dense fog to develop (with cigs lowering to the surface... thus fog). For now will mention areas of fog in the NW Piedmont and patchy fog elsewhere. Expect low temps in the heart of the CAD to move little overnight, maybe lower 2 to 4 degrees. Expect low temps will range from the mid 50s NW to the lower 60s SE/far E. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 240 PM Wednesday... Southwest flow at the surface and a little more westerly aloft, will result in a rapid dissipation of the CAD early Thursday. The ridge will be replaced by a surface lee trough of low pressure in the lee of the Mountains Thursday afternoon. Models suggest that the chance of showers and thunderstorms will be limited to the Mountains and NW Piedmont Thursday afternoon as weak instability develops along with surface moisture convergence along the trough. With heating, expect a chance of showers and thunderstorms, mainly west and north Piedmont zones. Much warmer conditions will advect into the region on the mean SW flow. Highs in the 80s are expected, except some upper 70s NW. The chance of showers/storms will diminish within a few hours of sunset Thursday evening, otherwise partly cloudy and warm conditions will exist in the developing warm sector of the next approaching front. Lows should stay 60+ Thursday night. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... As of 245 PM Wednesday... Fri: An approaching front will slow and become increasingly WSW-ENE oriented over the Mid-Atlantic by Friday as the parent cyclone becomes vertically stacked and temporarily stalls over the Great Lakes. As a result, southerly flow /above normal temps/ are expected to persist on Friday, albeit with an increasing potential for convection in the N/NW Piedmont during the late afternoon/evening. Sat-Wed: Potent shortwave energy moving ashore the Pacific coast tonight is progged to amplify into an upper low over the lower Midwest by Friday, track eastward through the TN valley on Saturday and progress across the Southeast CONUS on Sun/Mon, with shortwave ridging in the wake of the upper wave as it progresses offshore Tue/Wed. Confidence remains lower than average w/regard to forecast specifics (precip amounts, severe weather potential, temperatures) given that the aforementioned wave has yet to move ashore the Pacific coast. Until this feature is well sampled by the RAOB network over the western US, model guidance is likely to be in error w/regard to the evolution of the upper wave as it traverses the CONUS this weekend and early next week. Broadly speaking, expect mostly cloudy skies, cooler temperatures, and increasing chances for convection over the weekend, particularly on Sunday. Chances for precipitation will diminish from west-east and skies will clear early next week as the upper level wave progresses offshore, though confidence is low w/regard to when this will happen (as mentioned above), especially given potentially complex interaction with northern stream shortwave energy over the weekend. Some severe weather threat may exist over the weekend, however, it is difficult to ascertain whether or not such a threat will materialize at this range, let alone the extent/mode thereof. -Vincent && .AVIATION /06Z THURSDAY THROUGH MONDAY/...
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As of 215 AM Thursday... Areas of IFR and LIFR ceilings and some fog across much of the western and northern Piedmont including the KGSO terminal will persist overnight and expand east and southeast. VFR and MVFR conditions across the remainder of the Piedmont and the Coastal Plain including the KRDU, KRWI and KFAY terminals will deteriorate as low clouds and fog expand into the area overnight. Widespread IFR and LIFR conditions are expected during the few hours around daybreak. Light mainly southwest winds will weaken further and become calm in many locations providing additional support for fog development. Aviation conditions will improve between 13Z and 16Z as increasing sunshine and a westerly component to the low level flow results rising ceilings and erosion of the fog with the most aggressive improvement arriving after 14Z with just about all locations reaching VFR conditions by 16Z with SCT clouds at 4-5kft and periods of BKN clouds at 10-15kft. Southwesterly winds will increase to 7 to 10 kts this afternoon. Isolated showers and thunderstorms will develop across the NC mountains during the afternoon and push east possibly affecting the western Piedmont between 19Z and 23Z. Coverage and confidence in the amount of convection prohibits inclusion in the TAF at this time. Looking further ahead... A cold front will approach the region on Friday and then stall across northern NC Friday night and linger into Saturday and Sunday. A storm system will sweep east across the Carolinas late Sunday. These features will result in increased chances of adverse aviation conditions with sub-VFR ceilings with scattered showers and thunderstorms through much of the weekend. Improving conditions are expected on Monday. -Blaes
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Blaes NEAR TERM...BSD SHORT TERM...Badgett LONG TERM...VINCENT AVIATION...Blaes

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