Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 151730 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1230 PM EST Sun Jan 15 2017 .SYNOPSIS... A cold front will drop southward and exit the southern counties by early this evening. High pressure will build in behind the front and reinforce a cold air damming airmass over the area through Monday night. && .NEAR TERM /THROUGH TONIGHT/... As of 1035 AM Sunday... Little change in our sensible weather this afternoon. Early morning upper air analysis depicts a deep wly flow over the region with weak caa noted at 850mb. Moisture is mainly confined to the lowest 10k ft of the atmosphere, with the lowest 5k ft rather damp. Variably cloudy skies will persist with periods of partial sun more likely across the Sandhills and southern Piedmont compared to the rest of the forecast area. A surface cold front poised to enter our northern coastal plain counties late this morning will drift south-southwest this afternoon. Low level cold air advection behind this boundary fairly weak. Still, should see a wide range in high temperatures this afternoon across central NC,varying from around 50 in the far northeast, to the lower 60s across the southwest. If sun is more prevalent this afternoon across the south, high temperatures may end up being 3-4 degrees warmer than forecast. ~WSS Tonight: The cold front will push south of the area by this evening, with weak cold advection and a light northeast wind overnight. The H9 flow will swing around to southerly after midnight, resulting weak (and shallow) isentropic lift in the western Piedmont. As a result, some patchy light rain or drizzle should break out and drift east through the Piedmont through Monday morning, with low clouds eventually engulfing the entire area. Lows 38-45. ~SMITH && .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... As of 350 AM Sunday... CAD will persist Monday as the parent surface high shifts to the Mid-Atlantic coast and then eventually offshore. The main impacts look to be from just widespread low clouds since the H9-H85 flow is weak (< 30kt) and the flow aloft is flat. Low clouds will result in highs several degrees cooler than today, but the lack of precip should keep highs within a couple degrees but on the cooler side of guidance; 45-52. The aforementioned surface high will shift offshore Monday night, but our CAD airmass should linger without an erosion mechanism. Warm advection will start to increase over the western Piedmont, on the eastern flank of a prefrontal LLJ over the Tenn Valley. Most of the associated rain will be west of the mountains, but their could be a few areas in the Foothills and flirting with the western piedmont by Tuesday morning. Lows 42-46. && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 400 AM Sunday... The models are in relatively good agreement with the large scale pattern across NOAM through the start of this forecast period (early Tue), and this pattern will maintain continued cool and cloudy conditions --from in-situ CAD-- that will linger through midday Tue. A warming SSW low level flow will develop later Tue, and continue until a cold front accompanying a cyclone crossing the Great Lakes settles into the Srn Middle Atlantic states with an associated chance of showers centered around the day Wed. Primary forecast uncertainty for the remainder of the forecast period is how much nrn stream flow amplification of a series of nrn stream, split flow shortwave troughs occurs from Canada, and subsequently 1) to what degree they interact with a longer wavelength/less progressive srn stream, and 2) possibly slow and form a closed low across New England and the adjacent Canadian Maritimes. The handling of these features will play a role in the timing and degree of longwave riding and possible blocking over the ern U.S., and to what degree, if any, upstream shortwave energy can penetrate the ridge. It appears at this time that surface ridging, beneath the ridge aloft, will generally dominate late in the week and early next weekend, with one deamplifying shortwave trough likely to migrate into the ridge with an associated increase in cloudiness and chance of rain late Fri or Fri night. It will be a mild pattern, however, with temperatures remaining above freezing throughout the forecast period. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... AS OF 1230 PM Sunday... VFR parameters across central NC this afternoon will deteriorate this evening as a blanket of low stratus develops over the region. This deck of MVFR ceilings should begin between 00Z-04Z, with widespread MVFR ceilings by 06Z. In addition, should see patches of light rain develop over the western Piedmont after 00Z,some of which will cross the KINT and KGSO terminals. This added moisture will likely lower ceilings into the IFR category in the Triad after 06Z. The adverse aviation conditions with IFR/MVFR ceilings will persist through Monday and into Monday night. Ceilings may temporarily lift into the VFR category later Tuesday. However, aviation conditions will likely tank Tuesday night into Wednesday as a cold front approaches and crosses our region. Behind the front, VFR conditions anticipated for Thursday and Friday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...SMITH NEAR TERM...WSS/SMITH SHORT TERM...SMITH LONG TERM...MWS AVIATION...WSS is the U.S. government's official web portal to all federal, state and local government web resources and services.