Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 221822 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 122 PM EST Thu Feb 22 2018 .SYNOPSIS... An anomalous sub-tropical ridge aloft situated off the coast of the Carolinas, and related Bermuda surface high pressure, will weaken while drifting southwest toward the Bahamas through Friday night. Meanwhile, a back door cold front will settle south through central and southern VA today, and into north-central NC late tonight and early Friday. That front will become quasi-stationary over northern NC through Friday night, then retreat north as a warm front on Saturday. && .NEAR TERM /THROUGH TONIGHT/... As of 1015 AM Thursday... Little change needed to a generally persistence forecast for today -- almost identical to Wed-- with continued record-smashing sub- tropical high pressure centered near 31N/71W remaining influential throughout the southeastern U.S. It will consequently be very warm once again, with record temperatures in the mid 70s to lwr 80s, with partly to mostly cloudy conditions this afternoon. Morning upr air data indicate the subsidence inversion has indeed lowered, by about 3 k ft (down to 6 k ft), as the models indicated yesterday; and this will serve to further limit cumulus depth and shower potential today, despite the unseasonably warm and humid boundary layer. At the surface, a backdoor cold front analyzed at 15Z over cntl VA, just north of the Richmond, will continue to settle swd today, then reach the NC state line mid to late this evening. Thereafter, model guidance diverges with respect to how far south into NC the front moves overnight, despite very similar mass fields; and this will present the principle forecast challenge through the next 36 hours. At the present time, the thinking is that the front will stretch by 12Z Fri along an arc from near or just northeast of INT, to RDU, to PGV, to the srn Outer Banks. So for tonight, it will be continued unseasonably mild with generally upr 50s to lwr 60s and the redevelopment of fog and low stratus in the warm sector, with 50s and a slight chance of post-frontal rain/showers from a deeper, synoptically-driven low cloud layer behind the front. && .SHORT TERM /FRIDAY AND FRIDAY NIGHT/... As of 410 AM Thursday... Low Confidence in Friday`s forecast across central and northern Piedmont and Coastal Plain. Challenging forecast give the model discrepancy in the location of the back-door cold front Friday morning, with the NAM indicating a brief reprieve from the anomalous warmth, at least across the northern half of the forecast area, via a shallow in-situ wedge north of the boundary. Meanwhile, the GFS and EC stall the front briefly along the VA-NC border, keeping all of central NC in the warm sector. Huge bust potential wrt forecast highs Friday. If the NAM is correct, northern areas will struggle to get out of the 50s with some patchy drizzle possible through the first half of the day. Meanwhile, areas south of the front will once again warm into the mid to upper 70s. Am not ready to go quite that cool across the northern Piedmont, but have certainly trended towards the cooler guidance. Conversely if the GFS and EC verify, all of central NC will see another day of near record warmth with mid 70s to lower 80s everywhere. Lows Friday night ranging from mid 50s north to lower 60s south. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 330 AM Thursday... An unsettled pattern returns by the weekend, as a surface low is expected to strengthen across the central Great Plains States Saturday and eject northeast through the Great Lakes region on Sunday. This will push an associated cold front through central North Carolina Sunday and Sunday night before stalling it along the Carolina coast Monday. This front will re-introduce showers to the area as early as Saturday afternoon in the form of light pre-frontal showers, with the best coverage of rain, including the possibility of a rumble of thunder, arriving Sunday afternoon and evening as the front progresses through. Another wave will intensify along the front Monday and Monday night, spreading an additional wave of precipitation into the area. Some uncertainty here on just how far west this precipitation will spread, with some significant differences in the ECMWF/GFS solutions. The European solution tends to spread a greater amount of QPF inland, mainly due to a much slower progression of the original front, while the GFS keeps the bulk of the precip east of Interstate 95. For now, have kept PoPs higher in the southeast and lower in the northwest for this time period. High pressure builds in Tuesday and the first part of Wednesday keeping the area drier and temperatures much closer to normal for this time of year. The high will push offshore Wednesday afternoon ahead of a developing southern stream system set to introduce another round of rain chances Wednesday night into Thursday. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... As of 115 PM Thursday... Continued strong sub-tropical ridging off the coast of the Carolinas, and related Bermuda surface high pressure, will result in a mainly persistence forecast through the next 24 hours. Associated unseasonably humid conditions, on the wrn periphery of the ridge, will favor the redevelopment of low stratus (LIFR-IFR), and fog mainly at FAY, late tonight-early Fri. The low clouds, and fog mainly at FAY, will then lift and scatter to high MVFR or low VFR between 14-18Z. The exception will be mainly at RWI, where the IFR- MVFR stratus may linger throughout the day, and with a chance of light rain/drizzle in the morning, owing to the passage of a back door cold front in the few hours centered around 11Z, and following cool/saturated, post-frontal air mass. There is a slight chance that the front may pass through Piedmont sites and result in similar conditions there, but it is more likely the boundary stalls just north and northeast of INT/GSO/RDU. Outlook: The aforementioned ridge will weaken and drift south, but maintain influence over the Carolinas; and as such, a persistence forecast of late night-morning stratus and fog, lifting and scattering to high MVFR-low VFR each afternoon, will generally continue through the weekend. Otherwise, the next chance of rain will accompany a frontal zone that will settle into, and possibly stall over the Carolinas, late Sun into early next week. && .CLIMATE... RDU Records: Date | High Year | High Min Year ------------------------------------------ 02/22 75 1897 60 1897 02/23 79 1980 57 1962 02/24 81 1982 58 1985 GSO Records: Date | High Year | High Min Year ------------------------------------------ 02/22 74 1925 57 1980 02/23 74 2017 52 1922 02/24 79 1982 55 1985 FAY Records: Date | High Year | High Min Year ------------------------------------------- 02/22 77 2003 56 1989 02/23 80 1922 55 1922 02/24 83 1930 60 1975 && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...CBL LONG TERM...JJM AVIATION...MWS CLIMATE...RAH is the U.S. government's official web portal to all federal, state and local government web resources and services.