Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 211738 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 140 PM EDT Sat Oct 21 2017 .SYNOPSIS... High pressure will extend across the Carolinas through Sunday. A strong cold front will approach from the west Monday, and cross central NC on Tuesday. && .NEAR TERM /THROUGH TONIGHT/... As of 1005 AM Saturday... High pressure at the surface and aloft will remain in control of the weather through tonight across central NC. Aside from some passing cirrus, expect sunny skies and mild afternoon temperatures. Temps will average 8-10 degrees above normal for late October, ranging between the upper 70s-lower 80s. The sfc ridge associated with the high will drift offshore tonight through early Sunday. The resultant sely low level flow will advect enough warm moist air to produce patchy fog over sections of the coastal, plain, Sandhills, and potentially the eastern Piedmont by daybreak Sunday. Not expecting dense fog, so no travel issues anticipated. It will be a bit milder with low temps in the upper 40s to around 50 nw to the low-mid 50s southeast. && .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 /18Z SATURDAY THROUGH THURSDAY/... As of 140 PM Saturday... There is a high probability that VFR conditions will persist across central NC through 00Z Monday as high pressure at the surface and aloft controls the weather across central NC. The exception will be after 04Z tonight as patchy fog will develop, likely reducing the visibility into the MVFR range, particularly in vicinity of KRWI and KFAY, and possibly at KRDU. Pockets of IFR/LIFR visibility may occur close to daybreak in proximity of KRWI. Pockets of fog will disperse within an hour or sunrise. The good aviation conditions are expected to persists through early Sunday evening. Later Sunday night and on through Tuesday, an approaching frontal system will draw a moist low level air mass into central NC leading to an increased threat for sub VFR ceilings as well as increasing coverage of showers and a few thunderstorms, especially late Monday through early Tuesday. A return to VFR parameters anticipated for Tuesday night through Thursday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...MWS LONG TERM...BSD AVIATION...WSS is the U.S. government's official web portal to all federal, state and local government web resources and services.