Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 070705 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 205 AM EST Wed Dec 7 2016 .SYNOPSIS... Low pressure will move away from the Middle Atlantic coast tonight. Weak high pressure will follow and settle over the Carolinas through Wed night. An arctic cold frontal passage will occur on Thu. && .NEAR TERM /THROUGH TONIGHT/... As of 940 PM TUESDAY... All rain has departed the area as of 9 PM this evening, though overcast skies remain. Canadian high pressure will start building toward the region overnight as the surface low moves slowly away from Central NC. The pressure gradient between the two, particularly in the northeast portions of the area, will be a bit tight and result in winds in the 5-10 mph range through the night and at the start of the day Wednesday, light to calm in the west and south. The lows tonight will bottom out in the upper 30s to low 40s. The bigger forecast problem remains the development of fog overnight, possibly becoming dense in the west and southwest where winds are expected to be lightest. Patchy fog will be likely elsewhere given the very moist boundary layer. The fog should develop during the next couple of hours and will likely last through daybreak everywhere, except the far northwest where the boundary layer may dry out after 09Z. && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... As of 230 PM Tuesday... The leading edge of an arctic cold front diving southeast through the TN/OH valley begins to ooze across the Appalachians by 12Z Thursday morning. The front will be progressing slowly as it aligns with predominantly westerly flow, which will also serve to limit moisture advection available for precip. Forcing aloft will be limited as well in relatively broad cyclonic flow and channeled vorticity, with models squeezing out less than a tenth of an inch of rain with the system. As such will maintain only a small chance for PoPs as the front moves through during the day. Skies should be clearing from the northwest by mid to late afternoon. Cold air advection will be underway for much of the day across the northern tier with northwest winds 10 to 15 mph gusting 20 mph. This produces a low level thickness fall of ~20 meters across the north... indicative of 5-6 degrees cooler temps...resulting in highs from the low 50s across the north to upper 50s in the south. Pressure gradient relaxes overnight, but not enough to decouple and fully realize the airmass` potential for cooling. Mins should bottom out in the mid to upper 20s. && .LONG TERM /FRIDAY THROUGH TUESDAY/...
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As of 205 AM Wednesday... Expect cold/brisk conditions on Friday with highs in the upper 30s to lower 40s and a brisk NW breeze assoc/w strong cold advection as 1040 mb arctic high pressure builds eastward from the central plains toward the Appalachians in the wake of the cold frontal passage late Thu/Thu night. Expect chilly lows in the upper teens to lower 20s Sat morning as the arctic high settles over the Carolinas from the west Friday night, with highs on Sat similar to Friday albeit a few degrees warmer. Forecast confidence decreases significantly in the Sun-Tue time frame when the GFS/ECMWF differ by as much as ~24 hours with regard to the timing/evolution of the next upper wave/cold front approaching from the west. The GFS indicates a weaker, more progressive wave with an attendant cold front moving offshore Sun night. The ECMWF, however, indicates a more potent upper level wave /attendant sfc low/ and suggests the associated cold front will cross central NC Monday afternoon, exiting offshore late Monday evening into Monday night. With the above uncertainty in mind, will make little change to the prior forecast Sun-Tue. -Vincent
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&& .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... As of 1245 AM WEDNESDAY... In the wake of the low pressure system moving off the Mid-Atlantic Coast, drier air will filter into the area from the west, leading to scattering out of the IFR ceilings across central and eastern NC. However, light to calm winds in conjunction with wet soil, will lead to the development of fog. The lowest visibility/ceilings appear most likely to occur at INT and GSO, where restrictions could fall to LIFR. Any fog and low clouds will quickly disperse by 13 to 14z with VFR conditions expected through the afternoon. Outlook: A warm front will lift into NC and result in a good chance of MVFR ceilings Wed night-early Thu, especially at Ern TAF sites, followed by a small chance of a shower along an arctic cold front during the Thu, and following blustery NW winds late Thu afternoon- Thu night. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...KC SHORT TERM...MLM LONG TERM...Vincent AVIATION...CBL

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