Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 240251 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 950 PM EST Fri Feb 23 2018 .SYNOPSIS... A strong sub-tropical ridge aloft situated off the Southeast U.S. coast will weaken while drifting south toward the Bahamas through Saturday. Meanwhile, a quasi-stationary front will remain over central NC through tonight, then retreat northward while dissipating on Saturday. && .NEAR TERM /THROUGH TONIGHT/...
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As of 950 PM Friday... Just minor tweaks to the hourly temperatures required to the near term forecast. 00Z Saturday upper air analysis definitely depicts a weaker sub tropical ridge over the SE U.S. as heights are 20-40m lower compared to 12 hours ago. With a weaker high in vicinity, expect our stretch of unseasonably warm conditions to come to an end though temperatures tonight into Saturday will remain very mild for late February. At the surface ,a weak warm front extended west-to-east across central NC in vicinity of highway 64. This feature will continue to drift slowly north overnight before dissipating on Saturday. As nocturnal cooling continues, expect areas of low clouds to develop, initially across the northern Piedmont, then towards daybreak across the south and east. The formation of the clouds will cause temperatures to hold steady or actually rise a bit overnight. Min temps 50-55 across the north, and middle 50s across the south.
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&& .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... As of 340 PM Friday... Sub-tropical riding will remain centered in the vicinity or just northeast of the Bahamas, with associated surface high pressure extending from just south of Bermuda, wwd into the sern U.S. This pattern will maintain unseasonably warm and relatively humid conditions across cntl NC. Persistence high temperatures (relative to the warm sector) are expected to be in the mid 70s to around 80 degrees once again, given projected low level thickness values in the 1385-1390 meter range - very similar to Wed-Thu, and Fri in srn NC. While the sub-tropical ridge will also maintain a generally warm and capped environment to convection, small amplitude perturbations in swly flow aloft will glance the wrn and nrn Piedmont; and these may prove supportive of a few showers in a slightly less capped environment there. It will remain mild in steady swly flow Sat night, with low temperatures mainly in the lwr, to perhaps mid, 60s. && .LONG TERM /SUNDAY THROUGH FRIDAY/...
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As of 240 PM Friday... We remain in the warm sector for one final day Sunday with deep southerly flow on the west side of stacked ridging offshore. Highs Sunday will climb well into the 70s, with some very low 80s possible in the southeast. Moisture will be on the increase in this flow regime, and a cold front will be edging slowly east as the ridging offshore is flattened/suppressed south by a strong short wave moving across the Midwest and into the Great Lakes region. The surface front is expected to stall as it reaches the area on Sunday, with a surface wave lifting northeast up the frontal zone on Monday. Showers will thus be increasing from the west throughout the day on Sunday, becoming likely across all of central NC Sunday night through most of the day Monday. Widespread rainfall totals of one half inch are expected, but we could see one inch amounts due to training in some areas. Monday`s highs will be suppressed by rain in addition to cool air advection, but the encroaching airmass will be a bit warmer than seasonal, having originated in the lower Midwest and been allowed to further moderate due to slow eastward progression. High pressure will build into the mid Atlantic briefly Tuesday through early Wednesday, with plenty of sun and drier conditions to accompany seasonable temperatures in the low to mid 60s after morning lows in the 40s. A warm front will lift north, accompanied by increased cloud coverage and chances for showers by Wednesday afternoon through Thursday, when our next cold front is expected to sweep through and restart the cycle again. Highs Thursday will climb back to the 65 to 70 range ahead of the front, with seasonable temperatures near 60 to follow on Friday in the front`s wake.
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&& .AVIATION /00Z SATURDAY THROUGH THURSDAY/... As of 650 PM Friday... 24-Hour TAF Period: The front has stalled across Central NC, with KINT, KGSO, KRDU, and KRWI on the north side and KFAY to the south. As a result, a persistence forecast is likely at KFAY, with LIFR cigs and visbys developing overnight and into Saturday morning. Of lower confidence/higher uncertainty is the development of fog/low stratus on the north side of the front. If/when it does develop, it will likely do so between 07Z and 10Z, lingering into mid-morning at KRDU and KRWI, longer at KINT and KGSO (possibly into the early/mid afternoon). A brief 1-2 hr period of LIFR visbys is possible at all terminals, while the 300-800 ft cigs will last a while longer. Winds will generally be light and variable, increasing to around 10 kts out of the south-southwest at most terminals by the aft/eve hours Saturday. -KC Looking ahead: Increasing winds, particularly aloft, will limit fog potential Saturday night, except for at perhaps FAY and RWI where winds will be relatively lighter, with overnight-early morning low stratus anticipated otherwise and elsewhere. Those strengthening winds aloft may also result in marginal low level wind shear conditions at Piedmont sites Saturday night, given the likely presence of a shallow, ~1000 ft inversion, which will tend to separate a steady and even occasionally gusty ssw wind at the surface from an abrupt increase in flow within and above the inversion. The approach and slow passage of a frontal zone will result in a high probability of showers, and some sub-VFR conditions, late Sun into early next week. -MWS && .CLIMATE... RDU Records: Date | High Year | High Min Year ------------------------------------------ 02/24 81 1982 58 1985 GSO Records: Date | High Year | High Min Year ------------------------------------------ 02/24 79 1982 55 1985 FAY Records: Date | High Year | High Min Year ------------------------------------------- 02/24 83 1930 60 1975 && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...WSS SHORT TERM...MWS LONG TERM...mlm AVIATION...KC/MWS CLIMATE...RAH

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