Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 220837 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1253 AM EST Thu Feb 22 2018 .SYNOPSIS... Strong high pressure off the East Coast will hold steady tonight, then gradually weaken and drift southward Thursday and Friday. A backdoor cold front will enter northern NC by early Fri, and stall, then lift back north as a warm front Saturday. && .NEAR TERM /THROUGH TONIGHT/... As of 1015 PM Wednesday... Just small adjustments required to the near term forecast, primarily to the hourly temperatures. 00Z upper air analysis depicts an abnormally strong mid-upper level anti-cyclone with heights even above levels normally seen in the heat of summer. The sly flow around this system has pulled very warm and moist air into central NC, made evident by sfc dewpoints in the low-mid 60s. Typically, an air mass this moist would generate scattered showers; however, the atmosphere in the mid-upper levels is quite warm and dry, thanks to the subsidence associated with the upper level anti-cyclone. Main forecast challenge is the extent/severity of the fog expected to develop overnight. At 03Z, light sly sfc wind and temp/dewpoint spreads of 3-5 degrees suggest that fog formation will likely hold off until closer to daybreak. Since the set-up this evening is similar to conditions observed 24 hours ago, will likely see a deck of low stratus form/overspread the Piedmont counties, prohibiting fog formation. Across the Sandhills and coastal plain, fog development more likely with widespread vsbys 1-3 miles likely, with pockets of a half mile or less. Not anticipating a dense fog advisory at this time. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 400 PM Wednesday... A persistence forecast will be hard to beat for Thu, given only a slow weakening and swd retreat of the anomalous sub-tropical ridge off the sern U.S. coast. That is, low overcast and fog will gradually lift and morph into a mainly broken stratocumulus field through midday-early afternoon. The clouds will remain shallow and capped and unsupportive of precipitation, however, owing to a continued strong (and lowering per bufr forecast soundings) subsidence inversion related to the sub-tropical ridge. High temperatures should consequently again climb to record or nearly so values, in the middle 70s to around 80 degrees. A cold front, analyzed at 21Z from ern PA and NY swwd through cntl TN and the lwr MS Valley ,will have moved to near the Mason Dixon line by Thu morning; and this boundary is forecast to make slow swd progress across VA throughout the day. The NAM and GFS are very similar in their depiction of mass fields, but the NAM becomes most aggressive in driving the front into cntl NC Thu night. The NAM is preferred given superior representation of terrain and vertical model resolution in the low levels, which should best capture the associated shallow, post-frontal airmass. As such, the front is forecast to drift to near or just north of US Highway 64 by Fri morning, with continued mild upr 50s to lwr 60s and redevelopment of fog and low stratus ahead of it, and 50s and a small chance of post- frontal rain/showers behind it. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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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.
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&& .AVIATION /06Z THURSDAY THROUGH MONDAY/... As of 1252 AM Thursday... 24-Hour TAF Period: Southerly return flow between the offshore high pressure and a cold front approaching from the NW will continue to support an unseasonably warm and humid airmass, which will be prone to widespread stratus development, with MVFR generally between 06Z and 09Z Thursday, then subsequently dropping to IFR/LIFR between 09Z and 15Z, with the best chances at KFAY, then KRWI and less so at KRDU, KGSO, and KINT. Generally expect clouds to scatter out with bases in the 2-4 kft range by Thursday afternoon, though there is a chance KINT and KGSO terminals could stay broken into the afternoon. South- southwesterly winds will persist through the period, generally 5 kts or less overnight and 5-10 kts during the day Thursday. Looking ahead: A backdoor cold front will settle into at least nrn NC late tonight/Friday morning, roughly along or just north of US Highway 64. This boundary will result in a more prolonged period of IFR-MVFR ceilings along and north of it through most of the day Fri. Thereafter, 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. 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...
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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
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...MWS LONG TERM...JJM AVIATION...CBL/MWS CLIMATE...RAH

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