Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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898 FXUS62 KRAH 040548 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1245 AM EST Sun Dec 4 2016 .SYNOPSIS...
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High pressure will extend into the area from the north this morning. Low pressure will track from the Gulf Coast across the Southeast states late today through tonight, before moving off the coast Monday morning. High pressure will build in briefly from the north Monday afternoon, then a second stronger low pressure system will cross the Gulf States and Carolinas Monday night through Tuesday.
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&& .NEAR TERM /THROUGH SUNDAY/... As of 945 PM Saturday... High clouds continue to thicken in the wly flow aloft as the first in a series of s/ws shears out across the Deep South/southern Appalachians. This feature responsible for a few sprinkles skirting along the NC/SC border this evening. While upper levels have become quite moist during the past 245 hours, a decent layer of dry air still resides in the lower half of the atmosphere per 00Z GSO sounding. The passing of the 850/700mb ridge axis overnight will allow for better moisture advection by early Sunday, leading to increased chances for rain later Sunday morning across the western/southern Piedmont, and areawide Sunday afternoon-Sunday evening. Have adjusted PoPs overnight in the far west, and across the Piedmont Sunday morning based on observed radar/surface obs and trends of WRF/HRRR model runs. As cloud cover continues to thicken/lower, temperatures will slowly fall or hold steady overnight. Min temps lower 30s far north- northeast to the upper 30s south-southwest. ~WSS 340 PM discussion... First CAD event in quite a while expected to develop Sunday afternoon, with some rain and chilly temperatures. The 1028 MB surface high pressure extending from the Great Lakes SE through the Ohio Valley and into the central Appalachians will continue to move east to a position along the eastern seaboard Sunday. Dry and cool weather is expected overnight as high cloudiness is forecast to continue to overspread the region from the southwest. This increase in clouds is in response to the SW to NE mid/upper level jet extending across the southern tier of the U.S (out ahead of the deep west-central U.S. trough). This mid/upper level trough is forecast to lift NE during the next few days. In response, the surface high will align into a position that will extend down the eastern seaboard Sunday. This will set the stage for a Cold Air Damming (CAD) episode over the Piedmont Damming Region later Sunday into Monday. The strength of the CAD will be partly dependent on enough rain (QPF) to allow for evaporative cooling of the initially dry low level dry air in place. Models are in general agreement in a tenth to a quarter inch of rain (enough to allow for evaporative cooling and diabatic affects over the Piedmont Sunday and Sunday evening, which will lead to hybrid CAD conditions. This first shot of rain will occur with increasing moisture/lift with the approaching disturbance aloft Sunday, then aided by the WAA/ moist air being lifted up and over the coastal front and developing CAD. Models also suggest an initial weak surface wave to track SW to NE along the coastal front as well later Sunday and Sunday evening enhancing the rain. The higher QPF of near a half inch should occur near or just northwest of the coastal front where the convergence is maximized. Summary... tonight, increasing cloudiness with a light north breeze less than 10 mph. Lows generally 35-40. A few sprinkles possible late in the west. Sunday the WAA moist flow from the surface to H85 and developing mid level lift will lead to light rain developing/spreading NE across the region. Timing should bring highest POP to the west during the early to mid afternoon spreading throughout the entire region during the late day and Sunday night. Highs Sunday will be dependent on onset of rain and the amount of rain in the damming region. Highs should hold in the 40s Piedmont, with 50s SE. -Badgett && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY/... As of 340 PM Saturday... Rain Sunday night will taper to light rain or drizzle late as the initial surge of lift shifts to our NE and the initial wave of low pressure is forecast to move NE off the coast by 12Z/Monday. Temps should hold steady in the 40s/lower 50s NW to SE. The passage of the wave will bring a break in the rain chances for most of Monday. This occurs as another (this time weaker) surface high builds in from the north Monday. Some residual affects of the CAD should linger Monday in the heart of the Piedmont with plenty of clouds and some light mist or drizzle. Low clouds early may give way to breaks in the clouds around the edges of the damming Monday afternoon. However, we will undercut highs Monday going below statistical guidance by 5 degrees in the W-N Piedmont (near 50), but go close to guidance where breaks should occur (Sandhills, Coastal Plain) may see lower 60s. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... As of 400 PM Saturday... The parent storm is still expected to take on a "Miller B" scenario Monday night and Tuesday. This means the parent storm tracks NE from the Gulf of Mexico through the Ohio Valley Mon night. As this storm weakens, another develops along the SC coast (coastal front) and tracks along the NC coast Tuesday and Tuesday night. Another hybrid CAD event is expected as surface high pressure is forecast to become established from NY to western SC in the Miller B scenario. Lows Monday night generally in the 40s. Highs Tuesday will hold in the 40s in the Piedmont, with near 60 SE. Some lingering light rain or drizzle expected Tuesday night with temperatures holding steady or slowly rising. Ample moisture from both the Atlantic and Gulf will be pulled into the system and the result will be rain developing again Monday night and continuing Tuesday. The back edge or end of the significant rain should arrive very late Tuesday with models in general agreement on this timing. QPF this time should be heavier, with 1 to 1.5 inches expected. The first very cold air mass originating in Alaska and the Yukon will arrive in the mountains as early as Thursday. Models are trending faster and are more in line with the GFS (preferred solution) in pushing this air mass across the mountains to the coast late Thursday and Friday. Any showers would be rain and prefrontal in the warm air. Wednesday will be mild with decreasing clouds and temperatures in the 60s. Much colder temperatures are expected Thursday through Saturday with the heart of the cold for our region Friday into next weekend. Our coldest lows should be 20-25 and highs mid 30s to mid 40s Friday and 40-45 Saturday. && .AVIATION /06Z Sunday through Thursday/...
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As of 1245 AM Sunday... VFR conditions will hold through this morning across Central NC, although mid and high clouds will continue to overspread the area from the west. Cigs will stay above 5,000 ft AGL areawide through at least 17z. But conditions will gradually deteriorate this afternoon from SW to NE as surface low pressure and an upper level disturbance track across the Gulf States toward the Southeast. Cigs will drop to MVFR at INT/GSO starting around 18z with light rain spreading in, then at RDU/FAY starting around 21z, and at RWI starting around 02z this evening. Cigs are then expected to drop to IFR at INT/GSO after 21z and at RDU/FAY after 02z this evening. The rain will initially be light as it first arrives today with VFR vsbys holding, however as the rain intensity picks up a bit later today, vsbys will drop to MVFR in the late afternoon (INT/GSO) through evening (RDU/FAY/RWI). Winds will be light mainly from the NE initially before shifting to blow from the E and SE late today into tonight, remaining light. Looking beyond 06z late tonight, high confidence in poor aviation conditions, primarily IFR/LIFR cigs and MVFR/IFR vsbys, dominating later tonight through daybreak Mon. Rain will gradually taper off from NW to SE Monday morning with conditions rebounding to VFR areawide. VFR conditions will dominate from around 18z Mon until around 06z Tue. Then another storm system will cause IFR conditions to return after 06z early Tue morning, lasting through much of Tue with steady widespread rain returning. Rain will end late Tue, although IFR clouds will hold into Tue night. Improvement to VFR is expected Wed, then will drop back to MVFR/IFR Wed night. Cold front passage may bring VFR conditions once again Thu. -GIH
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...WSS/Badgett SHORT TERM...Badgett LONG TERM...BSD/Badgett AVIATION...Hartfield

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