Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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310 FXUS62 KRAH 231851 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 150 PM EST Thu Nov 23 2017 .SYNOPSIS... Initially cool high pressure will weaken and modify as it expands east across the middle Atlantic and southeast states through Friday night. Meanwhile, at least a couple of areas of low pressure will track from the eastern Gulf of Mexico northeastward across FL and offshore the southeastern US coast. && .NEAR TERM /THROUGH TONIGHT/... As of 1224 PM Thursday... Morning analysis shows plenty of cirrus moving up from the south, ahead of the short wave over N FL. This cirrus is thickest from about the I-95 corridor eastward, then thins out westward. Our current forecast anticipated this cirrus arrangement, thus our temp forecast reflects slightly warmer temps (due to more abundant sunshine) across the western Piedmont and Triad compared to locations farther east. Otherwise, we`re still looking at fair weather the rest of today. However its worth noting that the latest HRRR shows that the western edge of the light rain shield that`s currently located over coastal sections of SC will eventually lift north and may slide across our far SE zones, mainly southern Sampson Co. If this trend continues, we may have to put a slight chance PoP across that area for this evening...but fortunately any rain that falls there should be very light and short-lived (only a hour or so later this evening). Prev disc as of 345 AM Thursday...WV satellite imagery this morning depicts a positively-tilted longwave trough stretching from Atlantic Canada swwd across the cntl Appalachians, Deep South, and swrn Gulf of Mexico. This trough will be reinforced through tonight, as a pair of notable shortwave troughs upstream, over the upr Midwest and nrn/cntl Plains, respectively, amplify sewd in nwly flow aloft. The models indicate the one now over the upr Midwest will phase with a perturbation lifting newd from the GOM portion of the positive-tilt trough, by tonight over the Carolinas. Model cross sections depict associated strong omega over cntl and ern NC through tonight, but all above 500 mb (centered between 300-400 mb). At the surface, an elongated 1024 mb ridge extending this morning from the lwr Great Lakes swwd into srn TX will continue to weaken and modify as it migrates ewd, and becomes centered over the srn middle Atlantic states by 12Z Fri. Meanwhile, a couple of areas of low pressure are forecast to track, along a frontal zone, from the ern GOM newd across FL and off the sern US coast. The main forecast problem and uncertainty will be how cirrus/ cirrostratus in swly high level flow downstream of the aforementioned positive-tilt trough axis may affect temperatures today, mainly over the ern half of the forecast area. Full sun temperatures would favor highs ranging from upr 40s north to middle 50s, but the considerable high cloudiness may serve to keep temperatures in the srn and cntl Coastal Plain closer to 50 degrees. The high clouds will edge ewd overnight, as the upper trough axis likewise progresses ewd, with associated strong radiational cooling supportive of upper 20s to lower 30s, highest with longest-lingering high clouds in the Coastal Plain. && .SHORT TERM /FRIDAY AND FRIDAY NIGHT/... As of 400 AM Thursday... Weak shortwave ridging will briefly build across the Appalachians, between a positively-tilted trough axis forecast to progress to the coast through the day Fri, and a quickly-following trough forecast to amplify from the upr Great lakes to the lwr MS Valley through Sat morning. At the surface, high pressure will continue to extend swwd across the srn middle Atlantic states (including NC). Temperatures will consequently continue to modify in association with the surface ridge, with highs in the mid 50s to lwr 60s, and lows within a few degrees either side of 35. && .LONG TERM /SATURDAY THROUGH THURSDAY/...
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As of 150 PM EDT Thursday... Little change in longer range forecast. A mild day is in store for Saturday with a westerly flow ahead of an advancing, rather dry, cold front. Next area of high pressure will settle over the region Sunday through the middle of next week. The cooler temperatures behind the cold front Sunday and Monday will be rather short-lived as the upper ridge over the Western US transitions eastward atop the Eastern US by Tuesday/Wednesday. Highs Sunday and Monday in the low to mid 50s north to upper 50s south, then warming back up into the 60s and possibly even near 70 across the southern coastal plain and Sandhills by Wednesday. Model spread increases Wednesday and Thursday with the timing of upper trough ejecting out of the Rockies into the southeastern US. It still does not appear that this system will produce significant rainfall across the Carolina region.
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&& .AVIATION /18Z THURSDAY THROUGH TUESDAY/... As of 1224 PM Thursday... Through 24/18Z: High pressure will continue building over the area, resulting in light winds dry weather. Clouds will mostly consist of high clouds aoa 20k ft agl. VFR conditions through the 24 hour TAF period. After 24/18Z: A cold front will move across the region late Saturday and may bring a brief period of sub-VFR conditions during that time. Otherwise, VFR conditions expected through Tuesday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...np/MWS SHORT TERM...MWS LONG TERM...CBL/Franklin AVIATION...np

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