Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 150906 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 405 AM EST Wed Nov 15 2017 .SYNOPSIS... High pressure over the middle Atlantic states will weaken today, in response to the approach of an upper level trough that will cross our region tonight. The high will then linger over the southeastern US ahead of a cold front that will cross NC early Thu night. && .NEAR TERM /THROUGH TONIGHT/...
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As of 350 AM Wednesday... Shortwave ridging will briefly expand across the sern US and Carolinas today, downstream of an elongated and neutrally-tilted shortwave trough and embedded several perturbations now stretching from srn Manitoba to the cntl Plains. This trough will amplify across the upr Midwest/Great Lakes/OH Valley region through tonight, with associated 20-40 meter, 500 mb height falls expected to overspread cntl NC between 00-06Z Thu. Associated omega, and the depth of an associated mid-upper level moist axis forecast to sweep across the Piedmont between 03-06Z, before weakening, are greater than indicated by the models 24 hours ago. At the surface, 1029 mb surface high pressure centered over the nern US continues to extend swwd throughout the ern US this morning; and it will continue to do so over the Carolinas through tonight, while weakening owing to the aforementioned approaching mid-upper trough. Meanwhile, coastal frontogenesis and cyclogenesis will occur off the NC coast today, with the associated circulation center forecast to track briefly wnwwd to near or just offshore the NC Outer Banks by around 00Z, and to near the mouth of the Chesapeake Bay by 06Z Thu. Skies will start the day mostly sunny, except over the far nwrn Piedmont/on the ern edge of a blanket of stratocumulus banked against the Blue Ridge and trapped below a strong ~4 to 4.5 thousand ft subsidence inversion. However, a separate area of stratocumulus now stretching along the VA and nern NC coast will wrap wswwd into the nrn and cntl Coastal Plain and ne Piedmont in the several hours centered around noon. Cloudy or mostly so conditions are consequently expected to develop and prevail there throughout the afternoon, with a scattering of stratocumulus, and passing thin cirrus, elsewhere. High temperatures should accordingly reach the middle to upper 50s today, except ranging through the lower 50s, and to around 50 degrees toward Roanoke Rapids and Tarboro, for example. Given the aforementioned greater-than-earlier-indicated lift and moisture accompanying the approaching upper trough, a short period of sprinkles or light rain will be possible over the nw Piedmont this evening. Only virga is anticipated otherwise and elsewhere. West to east clearing overnight, and at least periods of calm amidst occasional light wswly stirring, will favor lows mostly 35 to 41 degrees.
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&& .SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
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As of 400 AM Wednesday... Nwly flow aloft will prevail this period, in the wake of the trough forecast to sweep across the nern quarter of the nation today and tonight. The ridge of high pressure now extending across the ern US will have weakened considerably and retreated into the sern states by Thu, ahead of a cold front approaching NC from the nw. This cold front, a moisture-starved one owing to the deep nwly flow aloft, will cross cntl NC Thu evening. It should warm nicely ahead of the front on Thu, with high temperatures well into the 60s (middle to upper), and some 70 degree readings possible from MEB to FAY to CTZ. Cooler behind the front Thu night, with lows mostly in the middle to upper 30s.
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&& .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 345 AM Wednesday... Dry and cool high pressure will build over the Atlantic coast on Friday with low amplitude, nearly zonal ridging aloft. Skies will be sunny with highs in the mid to upper 50s. This high will edge offshore Friday night, with mild temperatures and moisture advection in the resulting return flow on Saturday. Highs Saturday will climb to seasonable low and mid 60s after a morning low in the upper 30s. Concurrently, a strong short wave and associated cold front will be moving rapidly across the Ohio Valley, with the front`s racing across central NC Saturday night. The pressure gradient will tighten considerably ahead of the front, with low level jetting of 45 to 50 knots developing ahead of a very strong, but narrow zone of low level convergence. As such, expect that a vigorous line of showers will accompany the front, with strength of convection limited by the front`s unfavorable overnight timing and moisture availability limited by the front`s rapid movement. The front will be near the coast Sunday morning, with rapid clearing as early as late Saturday night in the west to Sunday morning in the east. Highs Sunday will be mostly low and mid 50s, as cold advection will produce only a modest rise from the morning mins which will be mostly in the lower 40s. The cool airmass will be in place Monday, with highs only reaching around 50 after a morning low around freezing. Dry weather will continue Tue and Wed, with highs edging to 50 to 55 after morning lows mostly in the lower 30s. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... As of 115 AM Wednesday... Stratocumulus, trapped below a couple of capping inversions between 3 and 5 thousand ft, will occasionally bubble over cntl NC through the forecast period, with the relative greatest coverage near and especially west of INT, and later today at RWI and perhaps as far west as RDU. The latter area near RWI will occur in association with, and on the west side of, an area of low pressure forecast to develop offshore and briefly approach the NC coast this afternoon, before lifting nwd along the middle Atlantic coast tonight. Outlook: The passage of a frontal system Sat night through early Sun will result in a chance of showers and sub-VFR conditions. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...MWS LONG TERM...mlm AVIATION...MWS

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