Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 211044 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 644 AM EDT Sat Oct 21 2017 .SYNOPSIS... High pressure will extend across the eastern United States through the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 345 AM Saturday... This discussion could be summarized in one word: persistence The models indicate the mid-upper ridge now over the sern United States will add about 20 meters as it builds to the coast of the Carolinas by tonight. At the surface, 1026 mb high pressure analyzed over the middle Atlantic states will likewise build ewd and offshore the middle Atlantic and Northeast coast, but continue to extend swwd across the sern US through tonight, and the remainder of the weekend. The result, as noted above, will be a generally persistence forecast, though with an increase in cirrus in wswly upper level flow that may yield a period of partly cloudy conditions this afternoon and evening. High temperatures are expected to again reach the upper 70s to lower 80s, while strong radiational cooling, perhaps delayed by cirrus early tonight, will favor low temperatures mostly in the mid-upper 40s to lower 50s. Persistence radiation fog centered over the Coastal Plain and far nern Piedmont will also again likely result. && .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... As of 355 AM Saturday... The mid-upper ridge in the vicinity of the coast of the Carolinas, and the associated surface ridge axis extending swwd into the sern US, will move little through the weekend. Persistence will still largely rule, although another day`s worth of ely low level flow around the ridge will have allowed surface dewpoints to climb more solidly into the 50s, to around 60 degrees or so in the Sandhills and srn Coastal Plain, by Sun evening. This will favor both slightly higher RH values than recent days, and also (mostly) few-scattered stratocumulus midday onward. Bufr forecast soundings from both the NAM and GFS suggest this stratocumulus may become broken in coverage/mostly cloudy by late afternoon-evening over srn portions of the RAH forecast area. Cloud cover, including some low clouds and fog centered again over ern portions of the forecast area, will further increase into the mostly cloudy range overnight, but the continued presence of a capping inversion aloft and lack of deep moisture, suggest conditions will remain dry. && .LONG TERM /MONDAY THROUGH FRIDAY/... As of 355 AM Saturday... Monday through Tuesday: Increasing southerly to south-southwesterly flow in advance of a deepening mid/upper level trough and potential closed mid level low over the lower MS valley region and deep south along with an approaching associated cold front will lead to a warm but cloudy weather on Monday. Chances for showers will increase across the western portion of the area by the afternoon. However, the main band of convection is expected to move across the area Monday night into Tuesday morning. Low level winds profiles will strengthen as the band of convection moves into and across the area, while the lead mid level impulse may attempt to take on a negative tilt. However, overall surface instability remains in question given the non-preferred diurnal timing (high shear, but low CAPE). With that said, instability is expected to remain rather weak and may be the limiting factor. Given the strong low and deep layer shear any surface based instability at all could prove very problematic, with the potential for damaging wind gusts and even a tornado or two. Stay tuned to this part of the forecast as a severe weather threat may be possible Monday night into Tuesday morning. Expect high temps on Monday will be warm in the 70s to around 80 SE, with lows on Tuesday morning generally in the 60s. The lead cold front and mid level dry punch is expected push the main band of convection to the east of the area by Tuesday afternoon (given the GFS and ECMWF current timing). This should end any severe threat, though temps will remain rather mild with any good CAA expected after sunset. Highs temps are expect to generally range from the upper 60s NW (which may come in the late morning or early afternoon) to the mid 70s SE/E. Tuesday night through Friday: Drier and cool weather is expected mid to late week as the deep/cold mid/upper level trough shifts across the area. This will result in quite weather during this period, with temps generally in the upper 50s to 60s for Wednesday and Thursday, with temps rebounding some into the 60s and 70s for Friday as surface high pressure shifts offshore. Low temps Wednesday morning are expected to be in the 40s NW to the 50s SE. Lows on Thursday and Friday morning are expected to generally range fro the upper 30s into the 40s, with some of the usual rural cold spots dropping into the mid 30s on Thursday morning if the MSLP gradient is able to relax enough. && .AVIATION /11Z SATURDAY THROUGH WEDNESDAY/...
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As of 640 AM Saturday... Under the influence of high pressure over the middle Atlantic states, persistence VFR conditions are expected to prevail, aside from late night-early morning radiation fog at RWI. In clockwise flow around the high, light nely to sely surface winds, are expected through the TAF period. Outlook: The threat of fog, and some associated low ceilings, will increase late Sun night-early Mon, owing to increasingly moist east to sely low level flow off the Atlantic ocean. An approaching frontal system will then result in the ewd progression of a band of IFR-MVFR ceilings, showers and isolated storms, and strong/shifting winds with height late Mon night through early Tue. Breezy swly winds will follow behind the associated cold front Tue afternoon.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...MWS LONG TERM...BSD AVIATION...MWS is the U.S. government's official web portal to all federal, state and local government web resources and services.