Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 200740 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 340 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/... As of 940 PM Thursday... Another night of calm winds and clear skies over central North Carolina. A slightly modified airmass that added a few degrees to our high temperatures today will do the same for the lows overnight. Expect most locations to bottom out in the 40s with some scattered upper 30s sprinkled in. && .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... As of 245 PM Thursday... The strengthening high aloft and associated subsidence coupled with the sfc ridge will maintain a dry atmosphere across central NC Friday and Friday night. This dry air will support diurnal temperature swings of 30-35 degrees. The warming aloft in conjunction with the ridge at the surface will translate to mild afternoon temperatures in the mid-upper 70s, with a few locations across the far south possibly reaching 80 degrees. While temperatures will be in the 70s late Friday afternoon, the dry air in place will permit temperatures to cool into the 60s early Friday evening, and solidly in the 50s by midnight. Minimum temperatures in the upper 40s to around 50 should be common. && .LONG TERM /SUNDAY THROUGH THURSDAY/...
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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.
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&& .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...Ellis SHORT TERM...WSS LONG TERM...np AVIATION...MWS

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