Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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238 FXUS62 KRAH 161540 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1040 AM EST Sat Dec 16 2017 .SYNOPSIS... High pressure will settle across the southeastern US through the weekend. A series of upper level disturbances will move through the region through mid week. && .NEAR TERM /THROUGH TONIGHT/...
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As of 1040 AM Saturday... Only a couple of minor changes were made to the near term forecast this morning. Sky coverage has been increased through tonight -- though still mostly sunny/clear through this evening-- based on the observed plume of cirrus on the nrn edge of the srn stream jet now lifting nwd across the TN Valley/srn Appalachians, and sampled by 12Z RAOBs most-applicably upstream at LZK, OHX, and MHX. High temperatures have also been raised up to a few degrees given that the observed subsidence inversion at GSO this morning was about 1000 ft higher than BUFR analysis/forecast soundings indicated; and this suggests mixing will be deeper today than forecast and consequently tap into warm(ing) air at the base of the inversion centered just below 850 mb. Previous discussion as of 350 AM Saturday follows... Surface high pressure over Alabama this morning will shift east and will become centered over the SE states late this afternoon and tonight, eventually shifting offshore Sunday. Meanwhile, +100 meter height rises and resultant strong mid-level subsidence inversion aloft will spread through the region today. This dry and subsiding airmass will result in dry conditions and abundant sunshine. While northern and central areas will see modestly warmer temperatures today, the southeastern tier will actually see slightly cooler readings than on Friday. Highs ranging from upper 40s/near 50 north to lower 50s south. As the closed low over Mexico opens up and ejects NEWD into the Southern and Central Plains overnight, high- level moisture will spread northeast into the area. These high clouds should have little to no bearing on min temps overnight. Lows in the upper 20s to lower 30s, with some mid 20s possible in the typically cooler locations.
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&& .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... As of 350 AM Saturday... Aforementioned southern stream trough will undergo further de- amplification on Sunday, shearing apart as it phases with the northern stream trough across the Ohio Valley. Associated slug of mid-level moisture will spread east, atop the mid/upper level ridge in place across the SE US. Fcst soundings suggest these clouds could be sufficiently opaque and thick enough to temper daytime temperatures, especially across the western Piedmont where earlier arrival would more readily coincide with peak afternoon heating. Highs ranging from lower 50s NW to upper 50s south. Surge of H8 warm moist advection on the northern periphery the low to mid-level ridge axis and along the leading edge of a 30 to 35kt nocturnal low-level jet could result in an isolated shower or sprinkles across the far southern zones Sunday night. Otherwise, cloudy with much milder lows generally in the 40s. && .LONG TERM /MONDAY THROUGH FRIDAY/... 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. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... As of 733 AM Saturday... Through 12Z Sunday: High confidence that VFR conditions associated with surface high pressure over the area will persist through Sunday. Looking beyond 24 hours: Low-level moisture return on the leading edge of a SWLY low-level jet could produce a brief period of MVFR ceilings Sunday evening and Sunday night. Additionally, lingering low-level moisture invof of a northward lifting warm front could potentially support periods of sub-VFR ceilings, especially at KFAY Monday and Tuesday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ NEAR TERM...MWS/CBL SHORT TERM...CBL LONG TERM...KC AVIATION...CBL is the U.S. government's official web portal to all federal, state and local government web resources and services.