Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 041137 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 635 AM EST Sun Dec 4 2016 .SYNOPSIS... 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. && .NEAR TERM /today through tonight/... As of 245 AM Sunday... Surface high pressure nosing southward from the central Appalachians into central NC is capped by a broad mid level ridge axis this morning, however this will soon give way to deepening moisture as the axes of both ridges shift eastward and IVT strengthens over the area, with the arrival of a weak mid level perturbation which flattens the mean flow over our region. Somewhat deep but weak moist isentropic upglide is already underway across western NC into the western/southern Piedmont, topped by weak upper divergence, although the subcloud layer here remains fairly deep, causing precip to be light and more patchy. This scenario should persist through much of this morning as the initial forcing for ascent will be rather weak with high cloud bases. But models show upglide gradually strengthening through the 285K-305K depth by early afternoon and remaining strong and deep over central/eastern NC from mid afternoon through much of tonight, coinciding with the west-to-east passage of the 850 mb SSW-erly jetlet across GA and the Carolinas, as well as with weak low pressure tracking from the Gulf Coast across the coastal Carolinas. Expect rain chances to increase by midday to categorical SW ranging to just slight chances NE where the surface ridge will hang on longer, all in line with consensus of large scale models as well as recent CAM runs. This will be followed by a trend to categorical pops over all of central NC by mid-late afternoon, persisting through midnight. Expect amounts through tonight to range from around a half inch in the north to around an inch across the south. This upglide will diminish late tonight as the low level jet shifts to our east, with the onset of downslope-directed low level flow and the departure of the weak surface low and weak mid level wave. Expect pops to trend down to chance NW but stay categorical in the SE until just before dawn. Below normal thicknesses with clouds and rain falling into a lingering stable pool favor chilly highs from the mid 40s NW to lower 50s E. Lows tonight 40-46. -GIH && .SHORT TERM /Monday through Monday night/... As of 305 AM Sunday... Much of Mon should actually be dry over central NC. Deep mid level low pressure over NW Mexico this morning will lift NE across TX through Mon, forcing a period of anticyclonic flow upstream over the Gulf/Southeast/Carolinas. The surface low will track NE away from the Carolina coast Mon morning with subsidence in its wake, as high pressure centered over the Ohio Valley into the central Appalachians builds in from the north, suppressing the frontal zone down across the central Gulf states. While there will still be a stable ridge nosing into the area, the lack of overrunning and brief period of subsidence aloft should generate a short-lived decrease in clouds and a lull in the wedge/damming regime. Expect highs mostly in the mid 50s. But rain returns Mon night as the potent mid level wave lifts NE through the lower Miss Valley, accompanied by a strong low at the surface, inducing a northward lift of the frontal zone. Moist upglide strengthens again rather quickly during the evening ahead of the mid level wave/surface low, as a 40-50 kt 850 mb southerly jet arrives from the WSW. Unlike late today/tonight when the best forcing for ascent (and hence most steady rain) will be focused across our southern half, on Mon night the entire CWA will see increasing PW to around 1.5" and much stronger upper divergence, so pops will increase SW to NE to categorical areawide by midnight. Expect 0.5-0.75" of rain overnight. Lows in the mid-upper 40s. -GIH && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 335 AM Sunday... The main weather maker for the period will be on Tuesday as a couple of low pressure systems affect the area in a Miller B type scenario with the main low pressure system tracking west of the Appalachians and a coastal low forming along the Carolina coast. This storm will have the most moisture available in recent memory and significant precipitation is expected with a widespread 1-2 inches of rain possible beginning late Monday night through Tuesday night. While the storm progresses to the northeast, a wedge will remain in place for much of the day keeping temperatures very cool, particularly in the Triad where highs will struggle to get into the mid 40s. There will be a large temperature gradient across the CWA as warmer air filters in with the coastal front and highs on southern and eastern fringes of the area could reach the upper 50s. The rain will end Thursday night as the system heads to the northeast. Lows in the upper 30s to low 40s. Wednesday and Thursday are expected to be dry and warmer with highs in the mid to upper 50s both days as the warm sector moves overhead in front of a longwave trough that will move across the plains and bring much colder temperatures to the area by Thursday night into Friday. The timing of this feature is quicker in the GFS solution and it is also drier as it moves through the area. The ECMWF solution lags the front and allows for significant development of the front with Gulf moisture. This scenario seems to be an outlier when compared to ensemble means and so the thinking at this time is for the drier/colder scenario seen in the GFS to prevail but I wouldn`t be surprised if the timing is a little fast, as can be the case with the GFS. Lows Thursday night in the mid 20s to low 30s with highs on Friday in the upper 30s to lower 40s. The cold drier airmass persists with the coldest lows of the period on Friday night with 20-25 degrees expected across the CWA. Only slight warming for Saturday with highs in the lower 40s. && .AVIATION /12Z Sunday through Thursday/... As of 635 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. Confidence is high in poor aviation conditions (primarily IFR/LIFR cigs and MVFR/IFR vsbys) dominating through daybreak Mon. 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 early 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 12z Monday morning, rain will gradually taper off from NW to SE Monday morning with conditions slowly rebounding to VFR areawide from west to east during the morning. 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 && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...Ellis AVIATION...Hartfield

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