Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 261901 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 300 PM EDT Wed Jul 26 2017 .SYNOPSIS... A stalled surface front draped across SC will return north as a warm front later tonight, then dissipate over central NC on Thursday. A cold front will approach from the northwest Thursday night and cross our region Friday night. && .NEAR TERM /THROUGH TONIGHT/... As of 255 PM Wednesday... A return to a typical summertime weather pattern to occur this period with an increasing chance for scattered convection in the short term. A strong upper level ridge extends west-to-east across the southern tier of the U.S., with the eastern extension across the Carolinas this afternoon. This upper ridge extension will weaken/retreat west as a series of disturbances in the jet stream across the northern tier of the U.S. begin to carve out an upper level trough along the eastern seaboard. The attendant sfc high will continue to drift offshore tonight through early Thu. The return sly flow will advect a more humid air mass residing across GA/SC, characterized by dewpoints in the lower 70s, into central NC by Thu. The stalled boundary delineating the northern extent of the humid air mass will advance northward overnight into central NC, then become ill- defined. This feature may trigger an isolated shower or storm this evening over the southern Piedmont. Overnight temperatures will be within a degree or two of 70 degrees. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
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As of 255 PM Wednesday... The atmosphere over central NC will become increasingly moist and unstable as the upper level ridge departs and height falls occur ahead of the approaching upper disturbances and sfc cold front. While an isolated storm or two possible in vicinity of the VA order Thu afternoon, better forcing/support aloft doesn`t arrive until Thu evening/Thu night. The atmosphere by late Thu projected to be slightly unstable with MLCAPE values approaching 1000 j/kg across the northern counties. Meanwhile, bulk shear not too shabby for this time of year, in the neighborhood of 25-30 kts. This could be supportive of broken line segments and potential strong wind gusts. This threat for strong storms should be isolated, however, and primarily confined to locations along and west of I-85 Thu evening. The threat for isolated/scattered convection will persist well into the overnight Thu night across our northern counties, particularly near the VA border as the initial disturbance crosses VA. Will maintain chance PoPs for now roughly north of highway 64 but may need to bump up PoPs in proximity of the VA border to likely after 06Z Fri, especially if the GFS verifies. The warming/modifying air mass will result in afternoon temps Thu near 90-lower 90s. Variably cloudy skies and continued light sly sfc wind will maintain warm/muggy conditions Thu night. Min temps generally in the lower 70s.
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As of 300 PM Wednesday... A vigorous mid-level shortwave will dig SE across the Ohio Valley and slow as it starts to cut off and reaches the mid Atlantic early this weekend. It will continue digging at this slowed pace SE across the area, exiting the coast on Sunday. A surface low will develop over northern Virginia along the cold front associated with this system on Friday, with NC remaining in strong warm and moist advection ahead of the front through the day. Convection will become likely by Friday afternoon with low level flow increasing convergence along the Piedmont trof ahead of the front, with likely PoPs lingering through frontal passage...which will be around midnight in the northwest, and near daybreak Saturday in the coastal plain. Stronger shear will remain north of the area in the vicinity of the triple point low and stronger upper diffluence associated with the upper short wave as they skirt northern Virginia. Strong instability with deep moisture could potentially produce a few severe storms capable of damaging downdrafts. Still a lot of uncertainty as to where it will concentrate, but convection will be widespread, so stay tuned. Highs Friday will be hindered by cloud and precip coverage, with the northern tier stalling out in the mid 80s, while some morning sun should produce some low 90s across the south. Could see patchy showers and maybe an isolated storm on Saturday as the upper trof swings through, otherwise clearing with a drier and cooler airmass settling into place which will linger at least through early next week. Lower humidity will add to the comfort level as highs Saturday through Tuesday top out mostly in the mid 80s, with a possible warmup towards midweek bumping highs back into the upper 80s Wednesday. Mins will be in the mid to upper 60s.
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&& .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... As of 1230 PM Wednesday... An area of high pressure extending across central NC this afternoon will provide VFR conditions through Thursday. The exception will be pockets of MVFR/IFR visibility due to fog overnight tonight through daybreak Thursday or patches of MVFR ceilings. The fog appears most probable in vicinity of of KFAY and KRWI between 09Z-12Z Thu. While VFR parameters anticipated for much of Thursday, an approaching cold front will increase the risk of scattered convection across the northern counties late Thursday but more so Thursday night. At this time, it appears scattered convection may be in the vicinity of the Triad terminals and KRDU after 02Z Friday, persisting into Friday morning. Additional scattered convection and associated MVFR parameters appear probable across central NC Friday through Friday night as the sfc cold front drifts southward. A drier, more stable atmosphere and attendant VFR parameters expected Saturday through Monday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...WSS LONG TERM...mlm AVIATION...WSS is the U.S. government's official web portal to all federal, state and local government web resources and services.