Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 041655 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1155 AM EST Sun Dec 4 2016 .SYNOPSIS...
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Cold air damming surface high pressure will extend into the area from the north into this evening as low pressure develops along the Gulf Coast. This weak low pressure will track NE along a coastal front tonight and offshore Monday. 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 TONIGHT/...
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As of 1155 AM Sunday... ...Cold air damming rapidly setting up over interior areas of NC... As expected, surface high pressure (of sufficient strength - greater than 1025 MB)and preferred location (extending from NY state south into the Carolina`s) to deliver a CAD event for our region, has evolved. The center of the high pressure was located over central PA into central VA (1027 mb) at noon. CAA and even dry air advection(DAA)continued over our region. The dry air source over VA reported dew points in the 25-30 range. This dry air was still being pushed into our region. Meanwhile, areas of rain continued to develop/spread NE and E from the Gulf Coast states through the TN valley and across the southern Appalachians due to the approaching disturbances in the mid/upper jet stream. While near saturation has occurred over much of western and southern NC where current readings ranged from 33-40 (a very chilly rain), areas in the north and east yet to see the rain begin still have a way to go to reach saturation. In other words, evaporative cooling will strongly ensue this afternoon as the rain fills in over the region from WSW to ENE. Expect highs to occur very early this afternoon, with falling temperatures this afternoon as the rain increases. Highs have probably already been achieved in the Triad and in the Sandhills (40- 45) and they have the potential to fall into the upper 30s this afternoon in the entire Triad region. To the east, expect rain to develop and overspread the region (very light at first, becoming steady later in the afternoon). As this occurs, the temperatures will fall from the 45-50 range early afternoon into the lower 40s later. As for QFP, expect a general 0.10 to 0.25 in the NW ranging to 0.25 to 0.50 in the SE for storm totals (just through this afternoon and tonight) - the next system will affect us with significant rain later Monday into Tuesday. See discussion below. The latest radar and satellite data are in good agreement with the overall rain system, with the steady rain expected to affect most of our region mid to late afternoon through the overnight, tapering off from the west overnight, leaving areas of mist and drizzle. The Cold air damming will be locked in place tonight. As temperatures are expected to fall into the upper 30s NW and lower to mid 40s SE through the afternoon. As the saturation is reached and the parent high shifts offshore tonight, temperatures will steady out at those upper 30s to lower 40s in the early evening, then remain overnight. Some dense fog may develop later tonight as the main lifting mechanism passes and the rain ends. This will leave low overcast with areas of fog and drizzle for the morning commute.
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&& .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...Badgett NEAR TERM...Badgett SHORT TERM...Hartfield LONG TERM...Ellis AVIATION...Hartfield

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