Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 160744 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 244 AM EST Sat Dec 16 2017 .SYNOPSIS... High pressure will move across the southeastern US through the weekend. && .NEAR TERM /TONIGHT/... As of 930 PM Friday... WV satellite and 00Z upr air data depict a nrn stream perturbation migrating enewd across wrn VA and NC, which has resulted in the ewd progression, and departure from cntl NC ,of the earlier mid-high level ceilings. This clearing trend will continue, with a steady ewd progression of the wrn edge of those ceilings fully out of cntl NC during the next few hours. Clear skies, in strong subsidence and height rises aloft centered over the upr Midwest and mid MS Valley -- in excess of 100-120 meters at 500 mb-- will follow for the overnight. At the surface, 1026 mb high pressure now-centered from the TX Gulf coast to wrn MS will expand newd tonight, behind a cold front that has just moved ssewd and offshore the sern NC coast in the past hour or two. Surface winds have already gone calm throughout much of cntl NC this evening; and any remaining nwly stirring should likewise subside overnight, as a portion of the aforementioned ridge "breaks off" over the Carolinas, separated by a sharp lee trough tucked tightly in the immediate lee of the Appalachians. As such, radiational cooling tonight should be strong, with associated low temperatures mostly in the middle 20s to around 30 degrees, though typically cooler sites like TTA and SCR, both of which were already down to 27-28 degrees at 02Z, may dip to near 20 degrees. && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... As of 153 PM Friday... Tranquil weather expected during this time with NW flow and mid/upr short wave ridging, and high pressure over the area. This will result in ample sunshine on Saturday. Skies will become partly cloudy Saturday night as high clouds move up into our area from the south. Forecast soundings and thickness profiles suggest subtle and gradual warming tomorrow. Highs Saturday from around 50 north of I- 85 to lower-mid 50s south. Lows Saturday night around freezing. && .LONG TERM /MONDAY THROUGH FRIDAY/...
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As of 243 AM Saturday... There continue to be significant fluctuations in the precipitation and temperature forecasts for the extended period as the medium- range models are having are still exhibiting differences from one another, particularly with a low/wave moving from the Southwest US toward the Mid-Atlantic. For now, expect temperatures well above normal through Tuesday night, highs in the low to mid 60s and lows in the 40s. Above normal temps will continue through the period, lowest Wednesday night/Thursday and moderating again thereafter. Best chances for rain will come Wednesday night into Thursday, although there will be at least a slight chance over portions of the area starting Tuesday night and lasting through Thursday night due to forecast uncertainty. A fairly complex upper level pattern unfolds during the extended forecast period. Monday, the high over the Caribbean ridges northward into the Mid-Atlantic region, while a cutoff low persists over the Southwest US/Baja/Northern Mexico and a low exists over central Canada. Over Central NC, the flow aloft will generally be zonal (west-east) through Tuesday night. The evolution of the upper level lows/waves and their interaction with one another will determine much of the weather for Central NC mid-week. It appears the ridge over Central NC will hold up against the deepening trough extending south-southeastward from the Canadian low Tuesday/Tuesday night. Meanwhile, the low over the desert Southwest will progress eastward into TX, then east-northeastward through the Midwest and into the TN/OH valley region through Wednesday. The model solutions really diverge with the evolution of this system beyond 00Z Wednesday, with the GFS more progressive/quicker and absorbing the low into the northern stream trough while the EC is slower and holds onto a closed low/shortwave longer and further north. With the continued differences, the temperature and precipitation forecast remain fairly uncertain for Tuesday night through Thursday. However, both models suggest the best chances for rain will be on Wednesday night/Thursday. Another trough/low will dig south out of Canada toward the Southwest US again on Thursday and Friday, resulting in a return to southwesterly flow and ridging aloft over Central NC. Differences also exist with regard to the surface pattern, but generally expect a stationary boundary in the vicinity of the Carolinas on Monday and Tuesday, with a Piedmont trough developing ahead of a stronger cold front to the north. The evolution/timing of the front differ between the GFS and EC. The GFS is faster/more progressive with the front moving southward through Central NC while the surface low moves across the Gulf coast and remains south of the region. The EC is slower with the approach of the front as the surface low is much farther north and approaches from the west, possibly moving over or just south of the area Wednesday night or Thursday. Both solutions forecast a wedge setting up late Thursday into Friday from High pressure over the Northeast US. Another cold front approaches from the west Friday and Friday night.
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&& .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... As of 100 AM Saturday... Through 00Z Sunday: High confidence that VFR conditions associated with surface high pressure over the area will persist through Sunday. Looking beyond 24 hours: A warm front lifting north into the area Sunday night and into Monday could bring a period of MVFR restrictions Sunday night and into the day on Monday. Lingering low- level moisture will continue to support periods of sub-VFR conditions, especially at KFAY through Tuesday night. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...np NEAR TERM...MWS SHORT TERM...np LONG TERM...KC AVIATION...CBL

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