Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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608 FXUS62 KRAH 231055 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 655 AM EDT Thu Mar 23 2017 .SYNOPSIS... Continental polar high pressure will continue to modify over the srn Middle Atlantic states through tonight. A warm front will retreat north across the region on Fri, as the high drifts east toward Bermuda. && .NEAR TERM /THROUGH TONIGHT/... As of 345 AM Thursday... 1034 mb high pressure now centered over ern PA and NJ will build south to the srn Middle Atlantic coast by this evening, beneath building heights aloft downstream of a progressive and increasingly amplified longwave ridge axis approaching from the central U.S. The presence of the surface ridge, one of cold and dry origin, will result in cooler conditions than previous days. High temperatures, unimpeded by occasional thin cirrus in NWly upper flow, will be in the 50s. A generally light ENEly wind may briefly gust to near 20 mph between 9 AM and noon east of I-95, with otherwise inconsequential gradually veering flow around the aforementioned surface ridge. The surface ridge will continue to extend across NC tonight. Associated calm to light ESEly surface winds, combined with a mainly clear sky aside from continued occasional thin cirrus, will favor strong radiational cooling and a light freeze away from urban centers; low temperatures in the upper 20s to middle 30s. && .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
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As of 355 AM Thursday... Surface high pressure will drift to near and just north of Bermuda; and associated return flow across the sern U.S. will allow a warm front to retreat north through central NC during the day Fri. Both temperatures and moisture will consequently be on the increase, with highs in the mid-upper 60s N and NW, to lower 70s in the S, and surface dewpoints in the 40s to near 50 degrees. The increasing low level moisture values, and broad WAA regime, will favor a scattering of flat/fair weather cumulus trapped beneath a subsidence inversion that will have become established courtesy of mid-upper level ridging aloft. Not as cool Fri night, though with decent radiational cooling potential as the Bermuda surface ridge continues to extend west into NC. Patchy radiation fog may result, with low temperatures in the middle 40s to around 50 degrees.
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&& .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 320 AM Thursday... The extended will primarily feature a Bermuda high and warm southerly flow, with highs in the 70s, at least 5-10 degrees above normal. Continued moistening Friday night may lead to some stratus near and west of the Yadkin River Saturday morning, and a pronounced cap will likely trap this moisture and yield partly to even mostly cloudy by Saturday afternoon. Meanwhile, and upper low over the Deep South will lift west of the mountains Saturday night, providing a glancing blow of DECENT height falls that should erode the cap and permit showers and storms, mainly west on Sunday. Current timing suggest early day clouds and showers, an extension of upstream convection on Saturday, may impede warming and destablization enough in the west to limit any severe with potential, though an axis of instability between the morning convection and the stronger cap to the east could support an isolated severe threat given 30-40kt bulk shear. The cold front associated with Sunday`s lifting upper low looks as though it will stay well west of the mountains and NC will stay in the warm sector, with another, less amplified system progged to cross the area on Tuesday. The latest ECMWF is much less amplified with this wave that it`s previous run, as well as the 00Z/23rd GFS runs. This system could be interesting given the potential for decent destablization in the warm sector on Tuesday and possibility of locally enhanced shear associated with the shortwave. For now, chance POPs still look most appropriate. After that, a backdoor cold front is forecast to sink south into NC by mid to late week, though the presence of the sub-tropical ridge makes frontal passage much less certain. && .AVIATION /11Z THURSDAY THROUGH MONDAY/...
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As of 650 AM Thursday... Continental polar high pressure over our region will result in VFR conditions through the TAF period. Surface winds around the high will generally be light and gradually veer from NEly/ENEly this morning to Ely/ESEly by this afternoon. The exception will be at FAY and RWI for a few hours mid to late morning, when winds may briefly increase to around 10-15 kts, with occasional gusts between 15-20 kts. Skies will be clear, aside from periods of thin cirrus. Outlook: There will be a chance of MVFR-IFR visibility restrictions in radiation fog in SErn NC (FAY and possibly RWI) Fri morning, then with patchy coverage throughout central NC Sat morning. A chance of showers and storms and sub-VFR conditions mainly at Piedmont TAF sites will follow for Sun.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...MWS LONG TERM...SMITH AVIATION...MWS

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