Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 061409 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 910 AM EST Wed Dec 6 2017 .SYNOPSIS...
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A cold front in eastern North Carolina this morning will move offshore late this afternoon. Cold high pressure will follow and extend across the Carolinas through Thursday. Meanwhile, a series of disturbances will pass overhead in southwesterly flow aloft.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 910 AM Wednesday... WV satellite and 00Z upper air data depict a lead, positively-tilted trough from Hudson Bay to srn CA, with an associated strong (100-150 kt) upper level jet extending from the Northeast to the srn Plains, including a srn stream jet streak now over the srn Plains and lwr MS Valley. This jet stream is forecast to migrate enewd and across the srn and cntl Appalachians late this afternoon and tonight. Meanwhile, a series of nrn branch polar and arctic stream perturbations were evident from the upr Great Lakes wwd along the US/Canadian border; and these are forecast to amplify a new, positively-tilted longwave trough from the Great Lakes to the Four Corners region by early Thu. At the surface, a cold front was across eastern North Carolina at 14Z this morning. A cP high pressure will follow and expand from the srn Plains today, to the srn Appalachians and Carolinas by tonight. Rain showers at 14Z in extreme eastern sections of the area will quickly move out of the area. Low clouds will dissipate as front and showers move offshore leaving a mid-level overcast over the region for the remainder of the day. Temperature trends today will reflect cold air advecting into the region. Readings will be in the 40s into the midday hours, followed by an afternoon recovery to into the upper 40s to lower 50s by this afternoon. The remainder of today should remain dry, though with probable virga falling from the aforementioned mid-high level ceilings, particularly late this afternoon when the upper jet streak now over srn plains is forecast to be streaming just nw of our region. Tonight: The drier and more sewd-suppressed model solutions are favored, best-represented by the 00Z ECMWF, owing to considerable sub-cloud dryness below maximum omega and saturation centered above 700 mb. Nonetheless, even the relatively drier ECMWF solution, which favors precipitation amounts ranging from just a couple of hundredths to to a tenth or two on the high end over the Sandhills and srn Coastal Plain-- would favor renewed (mostly light) rain spreading across roughly the sern half of the RAH CWFA, with the Triangle likely on the nwrn edge of the measurable precipitation shield. Again, this appears to be a classic, upper jet and mid level Fgen-generated light precipitation event, with precipitation falling from cloud bases mostly above 10 thousand ft. Low temperatures should dip relatively uniformly to around 40 degrees, with a small diurnal range governed by widespread cloud cover, and to a lesser degree evaporational cooling perhaps into the upr 30s where light rain occurs.
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&& .SHORT TERM /THURSDAY THROUGH SATURDAY/... As of 425 AM Wednesday... ...Potential continues for some wet snow late Thursday night and early Friday morning and especially Friday night and very early Saturday although the potential for accumulating snow is limited... An amplifying trough extending from eastern Canada southwest through the Great Lakes into west Texas on Thursday morning will shift east by Saturday morning. The main trough axis associated with an elongated and shearing shortwave trough will extend from near NYC southwest to the northeast Gulf of Mexico by Saturday morning. At the surface, a stationary front extending from northern FL northeast near but just off the Carolina coast lingers through Saturday with a couple of weak waves of low pressure developing and riding up the front. A secondary cold front with a surge of slightly colder and drier air pushes into the Carolinas on from the northwest on Friday. The persistent southwesterly flow aloft with deep moisture and multiple disturbances riding northeast over the baroclinic zone off the southeast coast will result in periods of precipitation across the coastal Carolinas and off the Coast for Thursday through early Saturday. Light rain is expected on Thursday morning across the Coastal Plain and Sandhills, mainly south and east of Raleigh. As disturbances aloft move up the coast, the precipitation shield will buckle northwest across most of the central NC including the Piedmont on Friday and Friday night with the most widespread precipitation and greatest precipitation amounts to the south and east of Raleigh. The precipitation will shift east late Friday night and Saturday morning with just some lingering, light spotty precipitation across the Coastal Plain expected early Saturday. With colder air working into the region, there is a chance that some of the precipitation will mix with or change to snow. It`s important to note that the pattern suggests an active period with widespread precipitation across coastal NC and decreasing amounts and coverage to the north and west in the more climatologically colder region of the northwest Piedmont. In addition, there is no well defined surface high to support the delivery of cold and dry air into central NC to support more than a low end event. Still, partial thickness values and forecast BUFR soundings support some wet snow across the northwest and northern Piedmont including the Triad area Thursday night and Friday morning with surface temperatures dropping into the 32 to 36 range. But given these areas are on the northwest fringe of the precipitation shield and PoPs are in only the chance range, have omitted any accumulation. A better chance for wet snow is expected Friday night and early Saturday morning across much of the Piedmont including the Triad and Triangle areas when the air mass will be a little colder. Air temperatures will fall into the lower 30s in these areas by Saturday morning which could support some light accumulations, on the order of a dusting, mainly across elevated and grassy locations in the general region of the I-85 corridor from Burlington northeast to the VA border. The warm boundary layer and ground temperatures combined with the limited precipitation amounts in the cold enough for snow areas should limit the amount, extent, and impact of snow accumulations. Highs on Thursday will range in the mid 40s with lows Thursday night in the 31 to 38 range. Highs on Friday will only in the lower 40s (may stay in the upper 30s in a few spots) with lows Friday night reaching 28 to 35 by Saturday morning. Cully on Saturday with highs in the lower to mid 40s. -Blaes && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... As of 430 AM Wednesday... Another potent short wave trough and potent lobe of vorticity will swing through the mid-Atlantic late Saturday and early Sunday. This feature will bring some enhanced cloud cover although moisture appears limited enough to preclude any precipitation. A northwest flow develops behind the trough on Sunday and continues into late Monday with dry and below normal temperatures. Another impressive trough approaches on Tuesday with a southwesterly flow ahead of the system that should allow temperatures to moderate and could bring some spotty precipitation before temperatures crash behind the trough on Tuesday night into Wednesday. -Blaes && .AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
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As of 910 AM Wednesday... A cold front was over eastern North Carolina at 14Z. The front and its associated rain showers will move offshore by late this afternoon. Drier low level air following the frontal passage will allow ceilings to lift into VFR range within a couple of hours after the frontal passage. The exception will be in the sand hills near KFAY, where MVFR ceilings are likely to be slower to lift into low VFR range - during the early-mid afternoon hours. VFR ceilings -- and periods of virga/precipitation aloft-- are expected to linger areawide through the end of the 12Z TAF period, as a series of disturbances pass in wswly flow aloft. Some of this precipitation will likely reach the ground and yield light rain mainly between 21Z- 04Z at KFAY, and perhaps as far nwwd as KRWI and KRDU, though with a progressively lower probability with nwwd extent. Outlook: An upper level trough will amplify west of the Appalachians, with associated periods of precipitation and sub-VFR conditions Thu through early Sat. Some of that precipitation may mix with or change to snow briefly at Piedmont sites, particularly at RDU and GSO, Fri morning and again Friday night-early Sat.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS/Franklin NEAR TERM...MWS/Franklin SHORT TERM...BLAES LONG TERM...BLAES AVIATION...MWS/Franklin

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