Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 162042 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 342 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 350 AM Saturday... Aforementioned southern stream trough will undergo further de- amplification on Sunday, shearing apart as it phases with the northern stream trough across the Ohio Valley. Associated slug of mid-level moisture will spread east, atop the mid/upper level ridge in place across the SE US. Fcst soundings suggest these clouds could be sufficiently opaque and thick enough to temper daytime temperatures, especially across the western Piedmont where earlier arrival would more readily coincide with peak afternoon heating. Highs ranging from lower 50s NW to upper 50s south. Surge of H8 warm moist advection on the northern periphery the low to mid-level ridge axis and along the leading edge of a 30 to 35kt nocturnal low-level jet could result in an isolated shower or sprinkles across the far southern zones Sunday night. Otherwise, cloudy with much milder lows generally in the 40s. && .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 /18Z SATURDAY THROUGH THURSDAY/... As of 120 PM Sunday... Under the influence of high pressure that will drift across the southeastern U.S., VFR conditions are anticipated through Sunday. A stream of initially thin, high-level clouds/cirrus, in association with a srn stream upper level jet, will gradually thicken (to ceilings) and lower to around 10 thousand ft by the end of the 18Z TAF period. Winds will be light swly to calm, on the nwrn periphery of the aforementioned surface high pressure over the sern states. Outlook: Ceilings will continue to lower, to between 5 and 10 thousand ft, Sun aft, with briefly widespread virga that may reach the ground in the form of patchy light rain or sprinkles between 18Z Sun-00Z Mon. The nwd retreat of a warm front, and leading edge of a more humid air mass, will result in a medium chance of advection fog and stratus Mon night, mainly at FAY. 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. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...np/CBL NEAR TERM...MWS SHORT TERM...CBL LONG TERM...MLM AVIATION...MWS

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