Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 170013 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 710 PM 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/... As of 340 PM Saturday... WV satellite imagery indicates a formerly closed mid-upper level low over nrn Mexico per 12Z RAOB data has begun to lift/shear newd and become an open wave centered over the Big Bend this afternoon, in response to the amplification of a strong, upstream shortwave trough toward the Baja of CA. This lead wave is forecast to have reached the mid MS VAlley by 12Z Sun, though with a fractured srn portion that will cross the mid South and have reached the wrn slopes of the srn/cntl Appalachians by the same time, while shortwave ridging otherwise expands across the sern U.S. At the surface, 1025 mb high pressure centered near ATL at 20Z will drift ewd, to the ern Carolinas by 12Z Sun. Meanwhile, a 1015 mb surface low just offshore the sern TX Gulf coast, and preceding maritime warm front, will surge newd across the lwr MS Valley. A plume of mid-high level moisture, downstream of the aforementioned lifting shortwave trough, will continue to blossom newd across the lwr-mid MS valley, then stream ewd across NC overnight, with resultant considerable high clouds and probable mostly cloudy conditions spreading into at least the wrn Piedmont late. Before that time and elsewhere, the nearby presence of the surface ridge, and initially thin cirrus early tonight, will favor strong radiational cooling conditions and lows likely in the middle 20s to around 30 degrees. && .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... As of 355 PM Saturday... The open wave now lifting across the Big Bend area will get strongly- sheared/crushed in confluent and zonal flow, across the OH Valley and middle Atlantic states Sun and early Sun night, then offshore. Associated weak height falls aloft, on the order of 10-20 meters at 500 mb, for example, will glance cntl NC in the several hours centered around 00Z Mon. Preceding mid-high level moisture that will have begun to stream into at least w-cntl NC late tonight will thicken and lower throughout the day. Ceilings will consequently continue to lower, to between 5 and 10 thousand ft after 18Z Sun, with associated widespread virga owing to strong omega and saturation in a mid-level mixed phase layer. Some of this precipitation aloft may reach the ground in the form of patchy light rain or sprinkles by late Sun afternoon and Sun evening, particularly across the nrn and nwrn Piedmont, where the aforementioned height falls aloft, and lift and saturation, are expected to be maximized. Skies may partially clear Sun night, though the approach of a maritime warm front from the Deep South may result in the redevelopment of clouds over srn NC late, though this time lower level ones in a several thousand ft layer centered around 5-6 thousand, with an associated slight chance of warm rain process light rain there, as a strengthening and increasingly moist wswly llj jet isentropically-ascends the retreating sfc frontal zone. The periods of cloudiness will likely affect both high and low temperatures, most notably over the wrn and nrn piedmont during the day, and over the srn Piedmont and Sandhills overnight. Highs 49 to 58 from nnw to sse; and lows from the upr 30s north to lwr-middle 40 south. && .LONG TERM /MONDAY THROUGH SATURDAY/... As of 330 PM Saturday... There has been a lot of north-south variation from model run to run in the position of the warm frontal zone over the past couple of days, but it looks like the moisture conveyor associated with a warm frontal zone will remain pinned south of the area during the early extended period. Low amplitude ridging and low level westerly flow will maintain our mild airmass with highs in the low and mid 60s both Monday and Tuesday. Min temperatures will be milder as well, with morning lows mostly low to mid 40s. PoPs both days will be in the slight chance range and limited to the southern tier counties. Ejection and subsequent eastward acceleration of a cutoff low over the 4 corners region will lift the frontal zone northward Tuesday night, with increased changes for showers Wednesday through Wednesday night as the dampening remnants of the wave move across the area. PoPs will still be focused across the southern tier, ranging from ~30% north to 50% south. Increased cloudiness and shower coverage will suppress highs on Wednesday to the mid and upper 50s, while modestly cooler air will settle briefly down the Atlantic coast in resulting northeast flow as the low moves offshore Thursday to produce highs mostly in the lower 50s. Reamplification of the subtropical ridge will result in a quick return to southwest flow with moisture on the rebound along with temperatures as we head into Friday and Saturday. Highs both days should reach 55 to 60, and the chance of showers will be increasing in the west Friday night, with chance PoPs across the area on Saturday. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/...
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As of 710 PM Saturday... VFR conditions will prevail through the TAF period. High cloudiness will continue to stream northeast, then east around mid level ridging into the area. The moisture plume will be deepening as a short wave moves across the southern Ohio Valley and redirects the moisture plume more directly into the area, resulting in ceilings lowering to the 5-10 thousand foot range by around 18Z Sunday. There could be fairly widespread virga that may reach the ground in the form of patchy light rain or sprinkles between 18Z Sun through 00Z Mon. Mid cloud ceilings will likely linger into at least early Sunday night until the short wave moves off the coast, suppressing a frontal zone and associated moisture feed south of the area. The moister airmass in vicinity of the frontal zone may result in some advection fog and stratus Mon night, mainly at FAY. Outlook: There will then be a high chance of rain and sub-VFR conditions, heaviest and lowest at FAY, late Tue night through Wed night, with the passage of a low pressure system across the sern U.S.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...np/CBL NEAR TERM...MWS SHORT TERM...MWS LONG TERM...MLM AVIATION...mlm/mws

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