Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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618 FXUS62 KRAH 200754 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 354 AM 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/...
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As of 340 AM Friday... Mid-upper ridging now centered from the delta of the MS River to the cntl Gulf of Mexico will amplify and build across the sern US through tonight, downstream of significant trough amplification from the Pac NW to the front range of the Rockies. At the surface, 1026 mb high pressure analyzed over the Cumberland Plateau will likewise build ewd, over or just east of the cntl Appalachians by Sat morning. With no change in, but another day of modification of, the air mass associated with that ridge of high pressure, temperatures today will be similar to, to perhaps a category milder than those of Thu. Patchy, thin cirrus in nly upper level flow this morning will get shunted offshore by this evening, as that flow backs to wly with the approach of the aforementioned upper ridge. As such, skies will be sunny/clear, except mostly so during the time of passing cirrus early today. Strong radiational cooling will favor low temperatures aob consensus statistical guidance tonight, mostly in the mid-upper 40s.
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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.
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&& .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 /06Z Friday through Tuesday/... As of 155 AM Friday... High pressure building east across the middle Atlantic states, and associated strong radiational cooling and risk of "persistence" (relative to similar conditions 24 hrs ago) radiation fog at RWI this morning, will otherwise result in mainly clear, VFR conditions with light and variable to light n/nely surface winds, through the TAF period. Outlook: Continued persistence radiation fog will be possible mainly at RWI each morning through the weekend, followed by a higher probability of more-widespread sub-VFR conditions in stratus and fog, in increasingly moist east to southeasterly low level flow, Sun night-Mon morning. An approaching frontal system will then result in a good chance of sub-VFR conditions, showers and storms, and strong/shifting winds with height late Mon-Tue. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...MWS LONG AVIATION...MWS is the U.S. government's official web portal to all federal, state and local government web resources and services.