Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 212337 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 637 PM EST Wed Feb 21 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 630 PM Wednesday... Just minor tweaks required to the near term forecast, primarily to lower or remove mention of the slight chance PoP along our western periphery this evening. An unseasonably strong sub tropical ridge centered offshore of the Southeast U.S. but extends back into the Carolinas and Georgia is the main weather feature controlling the sensible weather across central NC. The sly flow around this ridge is pumping warm humid air into our region, resulting in late Spring/early Summer warmth with the humidity to match. Record high temperatures were observed or tied at the three main climate sites. With loss of heating, lack of trigger mechanism, and relatively shallow layer of moisture have lowered the slight chance PoPs across the sections of the southern and western piedmont. Still cannot rule out a stray shower, mainly west-north of Winston-Salem this evening. A deck of low stratus will develop later tonight and cover most of the Piedmont, Across the Sandhills and coastal plain, areas of fog will develop, some of which may be dense in spots. Low confidence that an advisory for dense fog will be needed at this time. It will remain incredibly mild overnight with temperatures generally near 60-lower 60s. && .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 /FRIDAY THROUGH WEDNESDAY/... As of 230 PM Wednesday... At this time, current thinking is the cool wedge will settle as far south as US-64 Friday morning and gradually move northward Friday afternoon and evening. With that in mind, temperatures will remain in the 60s to the north of the boundary. In fact, readings near the NC/VA border may not get far above 60F. To the south of the wedge, maximum readings will climb to around 80F as high pressure off of the SE US coast strengthens and edges a bit further west. With such a tight temperature gradient on Friday, confidence is rather low. If the boundary does not move south into central NC on Friday, then temperatures in the northern Piedmont will be much warmer than forecast. A more unsettled pattern returns by the weekend, as a surface low is expected to strengthen across the central Great Plains by Saturday and eject northeast through the Great Lakes Region through Sunday. This will push an associated cold front through central North Carolina Sunday and Sunday night before stalling it along the coast Monday and Tuesday. This will reintroduce showers and possibly a few thunderstorms as early as Saturday afternoon in the form of pre- frontal showers, with the best forcing arriving Sunday afternoon and evening as the front progresses through. Another wave will intensify along the front Monday into early Tuesday before a cooler area of high pressure takes over, keeping conditions a bit more seasonable. Wednesday starts dry but rain showers may move into western sections by late in the day with warm air advection ahead of the next system. && .AVIATION /00Z THURSDAY THROUGH TUESDAY/...
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As of 635 PM Wednesday... 24-Hour TAF Period: VFR conditions to start the TAF period will once again give way to MVFR cigs and visbys after midnight, 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. -KC Looking ahead: 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. However, a backdoor cold front will settle into at least nrn NC on Fri, roughly along or just north of US Highway 64; and this boundary will result in a more prolonged period of IFR-MVFR ceilings along and north of it through most of the day Fri. 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. -MWS
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&& .CLIMATE... RDU Records: Date | High Year | High Min Year ------------------------------------------ 02/21 76 2011 55 1939 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 ------------------------------------------ 02/21 74 2011 50 1954 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 ------------------------------------------- 02/21 80 1991 61 1953 02/22 77 2003 56 1989 02/23 80 1922 55 1922 02/24 83 1930 60 1975 && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...MWS LONG TERM...JJM/Franklin AVIATION...KC/MWS CLIMATE...RAH

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