Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 201745 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 145 PM EDT Fri Oct 20 2017 .SYNOPSIS... A ridge of high pressure will extend across the eastern United States through the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 1015 AM Friday... Stacked high pressure over the Deep South/TN Valley will maintain dry and seasonably mild air mass over central NC this afternoon and tonight. The circulation around this high pressure system is resulting in a nw flow over our area. The downslope component of the low level flow along with modest compressional warming aloft will lend to a relatively warm afternoon with temperatures well into the 70s, and likely reaching 80 degrees across the southern Piedmont and the Sandhills. Presence of the low level dry air over the region will once again allow temperatures to cool quickly immediately after sunset, falling through the 60s in the early evening, and into the 50s by late evening. Overnight low temperatures in the 45-50 degree range. && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... As of 350 AM Friday... Mid-upper ridging will linger in the vicinity of the sern US coast, while high pressure drifts off the middle Atlantic and Northeast coast, while also strengthening. The result will be a generally persistence forecast, though with an increase in high cloudiness that may tip sky conditions into the partly cloudy range by Sat night, with associated slightly milder low temperatures in the upper 40s to middle 50s. High temperatures again in the middle 70s to around 80 degrees, or so. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 340 AM Friday... The ridge over the southeast will move east Sunday as a trough over the Midwest and Mississippi Valley deepens. We`ll have another nice day Sunday to round out the weekend`s weather, featuring partly cloudy skies (mainly high clouds) and return flow resulting in warm temps with highs in the upper 70s to around 80. Monday will feature increasing and lowering clouds as a closed trough ahead of the upstream longwave trough moves across the TN Valley and moist S/SW flow aloft increases over our area ahead of this trough. GFS and ECMWF solutions diverge Monday night and Tuesday. The ECMWF shows the lead short wave getting absorbed into the larger longwave trough and ejected to the northeast 12+ hours faster than the GFS. The ECMWF solution would result in a band of showers quickly moving across our CWA early Tuesday morning before exiting to our east by noon Tuesday. The slower GFS brings multiple bands of showers across our area Monday night through about mid-day Tuesday, with perhaps a brief opportunity for a few gusty tstms during the late morning Tuesday before the showers exit to our east. This thanks to the proximity of the passing mid-level trough and subsequent stronger wind fields and resultant shear; however GFS forecast sounding show limited instability, thus perhaps a high-shear/low- CAPE setup with isolated strong wind gusts the main concern if any severe weather threat materializes. Finally, there will be another brief opportunity for a few showers late-day Tuesday with the passage of the sfc cold front. Coverage and intensity should be limited though, thanks to the earlier passage of the lead short wave and subsidence and mid-level drying in its wake. Tuesday night we`ll drying and strong CAA commence in the wake of the cold front, with additional CAA behind the passage of the longwave trough axis which is progged to move across our CWA late Wednesday. The main weather story for Wednesday and Thursday will be the chilly temps, with highs only in the low 60s both days, and potential for lows dipping down into the upper 30s in some spots Thursday morning. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
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As of 145 PM Friday... There is a high probability that VFR conditions will persist across central NC through 00Z Sunday as high pressure at the surface and aloft controls the weather across central NC. The exception will be brief instance of MVFR/IFR fog in vicinity of KRWI and possibly KFAY between 06Z and 12Z Saturday. Otherwise expect clear-mostly clear skies and light winds, primarily out of the east-northeast, except calm at night. 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 Tuesday. Improving aviation conditions anticipated Wednesday as the front exits our region and chilly high pressure expands toward the Carolinas.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...WSS SHORT TERM...MWS LONG TERM...np AVIATION...WSS

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