Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 270603 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 203 AM EDT Thu Jul 27 2017 .SYNOPSIS... Surface ridge axis over the area will shift offshore later this morning. Meanwhile a stalled surface front draped across SC will dissipate today with a weak surface trough developing across the NC Piedmont this afternoon. A cold front will approach from the northwest Thursday night and cross our region Friday night. && .NEAR TERM /THROUGH TONIGHT/... As of 1005 PM Wednesday... 1022 mb surface high pressure along the nrn middle Atlantic coast will continue to extend swwd through the east-central Carolinas tonight. Return flow around the ridge axis, in a warm advection regime indicated by RAOB and VWP-observed veering low-mid level wind profiles over the wrn Carolinas and VA, will favor the development/percolation of areas of 3-5 thousand ft stratocumulus over central NC tonight. CAM solutions suggest some of these clouds may deepen into shallow showers overnight, capped above by a continued 8-10 thousand subsidence inversion aloft evident in both GSO and RNK 00Z-observed RAOB data, mainly over the wrn and nrn Piedmont (where the WAA regime will remain maximized). Isolated showers may consequently result there, with otherwise partly cloudy skies and lows in the upper 60s to lower 70s. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... 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. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... 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 warm up towards midweek bumping highs back into the upper 80s Wednesday. Mins will be in the mid to upper 60s. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... As of 203 AM Thursday... Weak return flow/WAA maximized across western NC, along the western periphery of the sfc ridge axis centered across eastern NC will result in 3-5 thousand ft stratocumulus across central NC overnight, with an isolated/stray shower possible near KINT and KGSO. Otherwise, expect predominately VFR conditions this morning and much of the day on Thursday with a broken stratocu expected owing to strong heating. KINT and KGSO will see the best chance of convection this afternoon, with upstream disturbances and associated convection expected to track SE into the western Piedmont during 20 to 24z time frame. Have included a prob30 group for thunder for this time frame. There after, confidence decreases with the evolution of this convection whether it will persist and advance east into the central Piedmont and coastal Plain or if it will weaken and dissipate altogether. There is also the potential for additional convection to to propagate east/se into the area Thursday night, especially across the northern terminals. Outlook for Friday through Monday... MVFR to IFR conditions associated with numerous showers and thunderstorms late Friday/Friday night as a cold front is expected to push SE through the area. Aside from some isolated convection Saturday night/Sunday as the upper low/trough digs south over the area, expect predominately VFR conditions through Monday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...CBL NEAR TERM...MWS SHORT TERM...WSS LONG TERM...mlm AVIATION...CBL

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