Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 031123 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 625 AM EST Sat Dec 3 2016 .SYNOPSIS... High pressure will build into the Carolinas from the northwest through Saturday night. A storm system will move from northern Mexico across Texas and the Gulf Coast states into the Southeast states Sunday through Tuesday, bringing unsettled weather for North Carolina. && .NEAR TERM /today through tonight/... As of 345 AM Saturday... Deep low pressure continues to dig over NW Mexico early this morning, and this low along with the preceding deep plume of moisture spreading into the TX/Gulf States and Southeast over the next couple of days will be the primary driver for our weather into early next week. The latest surface analysis shows a weak mesohigh over Central NC loosely connected to a larger high centered over the Mid Miss Valley. This general surface configuration will hold through today and tonight as the core of the larger high shifts NE through the Ohio Valley. Fast WNW mid level flow acting on a slug of high level moisture within a stable column have led to enhancement of cirrus in the lee of the southern Appalachians early this morning, which should linger at least into mid morning. Irrespective of this phenomenon, high clouds will gradually increase and become more opaque later today into tonight as minor mid level perturbations ride NE atop the flat ridge extending over the Gulf and Southeast states toward NC. But the persistence of dry low level air today will mean a dry forecast today. The decreased insolation compared to yesterday and lower thicknesses will result in highs today around a category lower than yesterday, in the lower to mid 50s. Cloud bases will continue to lower tonight with thickening broken to overcast decks overspreading the area, and while moist isentropic upglide does deepen, it remains rather weak and confined above 5000 ft AGL, which would seem to favor just patchy very light rain at most moving into the western Piedmont late tonight. Will keep very low chance pops in the far west only. Lows from 35 NE to near 40 SW. -GIH && .SHORT TERM /Sunday through Sunday night/... As of 405 AM Saturday... The deep low will wobble slowly across N Mexico toward TX Sun through Sun night, as surface frontogenesis ramps up over the Gulf Coast to the northeast, across GA/SC to the southern coast of NC. The east-northeastward expansion of what should be widespread rain from TX into the Southeast will initially be stymied by the surface ridge, which will extend from Ontario/Quebec southward into the area through much of Sunday, as well as by the effects of the broad mid level ridge, the axis of which will be passing over the Carolinas, limiting overall ascent. Will bring low chance pops into Central NC Sunday, ~30% chance west ranging to slight or no pops in the east where the relatively dry subcloud layer will be deeper. Thick clouds will further hold temps down, and expect highs from the mid 40s NW (beneath the most pronounced combination of thick clouds and cool/stable low levels) to the lower 50s SE. The arrival of a 40+ kt low level jetlet across GA/SC/NC Sun evening along with strengthening IVT will result in a ramping up of moist upglide and overall forcing for ascent, in tandem with the departure of the surface ridge, making the low levels vulnerable to saturation. Expect rain coverage to increase to likely in the NW CWA and categorical south/southeast Sun evening, followed by a slow exit later Sun night as the low level jetlet shifts to our east and deep moist upglide shuts down. Rainfall from late Sun through Sun night could approach 0.25-0.50", higher in the south. Expect lows from around 40 NW to mid 40s SE. -GIH && .LONG TERM /MONDAY THROUGH FRIDAY/... As of 325 AM Saturday... Monday will be a transitional day with high pressure moving off the coast, a weak wave along the coast and new high pressure moving into the mid-Atlantic region from the Ohio Valley. The upshot of this is that we will move from more of an in-situ damming situation to more of a hybrid scenario but northeasterly winds across the area and chances for precipitation early in the day with a lull later on. The cold air damming should keep temperatures down around 50 degrees in the Triad with middle 50s across the southeast. Tuesday the Miller B scenario takes full effect a pair of lows on either side of the wedge parked over the Piedmont. Precipitation should begin early Tuesday morning and continue all the way through Tuesday night before the system starts to move off to the northeast. Accumulations for this event should be over an inch and possibly up to two inches. Temperatures will be tricky and dependent highly upon the track of the coastal low. With fairly high confidence, the Triad should stay cold throughout the day under the wedge with highs possibly only in the upper 40s. The bigger uncertainties in the temperature forecast lay in the south and east where highs could be as much as 60 degrees. Wednesday and Thursday will be dry and a little warmer on the front side of a longwave trough bisecting the continent. Highs in the 60s. By Thursday night, models begin to diverge on timing and available moisture leading to two very different possible scenarios for Thursday night into Friday. The GFS solution has a very progressive trough and a drier solution which brings very cold temperatures into the area on Thursday night. The ECMWF solution is slower and wetter which means warmer temperatures hanging around longer Thursday night. For now we are taking the dry, colder forecast so expect temperatures below freezing both Thursday and Friday nights with Friday being the coldest as very anomalous thickness values move into the area and bring low temperatures down into the 20-25 degree range. && .AVIATION /12Z Saturday through Wednesday/...
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As of 625 AM Saturday... High confidence in VFR conditions for the next 24 hours. Surface high pressure will continue to build into the region today, with deep dry air as mid level ridging shifts over the Southeast states. Only a thin veil of high clouds is expected across the area today, although clouds will become more opaque with lowering bases to 12,000-18,000 ft AGL late today through midnight tonight as upper level perturbations emanating from the developing storm system over N Mexico track ENE toward the Carolinas. Mid clouds will continue to thicken and lower late tonight, dropping to 5,000-6,000 ft AGL by early Sunday. Surface winds will be light from the NW through daybreak, then from the NW around 8-10 kts through sundown, becoming light/variable once again tonight. Looking beyond 12z Sun: Patchy light rain will start to spread in during the day Sunday from the SW as the upper level disturbances break down the mid level ridge, although VFR conditions should hold for much of the day. Confidence is high that conditions will deteriorate further to IFR Sunday evening/night and remain poor at IFR or LIFR into early Monday with periods of rain, particularly south. Some improvement to MVFR or even briefly VFR on Monday, but should quickly drop again to IFR/LIFR Monday night into Tuesday evening with rain areawide. Rain should taper off Tuesday night but IFR/LIFR conditions may hold through daybreak Wednesday, followed by improvement to VFR by midday Wednesday. The potential for low level wind shear will remain a concern, especially Sunday night and again on Tuesday. -GIH
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...Ellis AVIATION...Hartfield

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