Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 270643 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 243 AM EDT MON SEP 26 2016 .SYNOPSIS... A cold front will stall across the Carolinas today through late in the work week, bringing unsettled weather through the period. && .NEAR TERM /OVERNIGHT/... As of 910 PM Monday Have adjusted PoPs upward over the western-nw Piedmont as a band of convection has arrived and has begun to slow its eastward progression. This is raising concerns for a localized excessive rainfall, mainly just south of Winston-Salem and Greensboro, encompassing Lexington and Asheboro, and west of RDU, affecting the Chapel Hill/Carrboro area. Some locations in the area described above may receive 2-3 inches of rain in less than 3 hours before 2 Am Tuesday. This may cause a few creeks and streams to leave their banks and may lead to an isolated road closure or two. Believe the threat is too isolated for a flash flood watch but will continue to monitor. The scenario is a classic set-up with a slowing band of convection becoming perpendicular to a sly feed of moist air. Tonight, this west-sw/e-ne band is encountering a sly south of 15-20kts in the 925- 850mb layer, advecting moist air with precip water values 1.6-1.8 inches, close to 150 percent of normal. Additional lift being supplied aloft by 100kt jet crossing the eastern Great Lakes, placing the nw Piedmont in the favored right entrance region. Farther east, mainly for areas east of highway 1, overcast skies and and a few spotty showers are expected though overall coverage and intensity are expected to be spotty and light. Overnight temps will be fairly uniform due to the overcast skies and light sly flow. Min temps mid-upper 60s. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... As of 250 PM Monday... The cold front will inch eastward into the Piedmont on Tuesday, slowed further by system parallel flow induced by the upper low that will close off and dig toward the Tenn Valley. PW will remain relatively high at 1.75", though the source of higher PW off the coast looks to be cut off by a surface wave that lights northeast along the NC coast. Forcing is pretty much limited to moisture convergence along the front, with better height falls later Tuesday night ahead of the aforementioned upper low. Despite weak lapse rates aloft, highs in the upper 70s/lower 80s should result in weak instability and trigger scattered to numerous showers and a few isolated, mainly in the Piedmont. Increasing mid-level wind fields will increase the shear over the region Tuesday afternoon, but weak instability (better Wednesday) will ultimately limit the threat of severe storms. Based largely on WPC guidance, 0.5-1.0" of rain is generally expected. As mentioned above, forcing aloft is a little better late Tuesday, albeit with less instability (though forecast soundings do show some thin MUCAPE that may enhance parcel lift). The front isn`t expected to make much progress eastward, so there may be a limited flooding threat worth watching Tuesday evening, largely dependent on how active the front is tonight and Tuesday. Lows again in the upper 60s. && .LONG TERM /THURSDAY THROUGH TUESDAY/...
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As of 245 AM Tuesday... An upper level low over the northern Great Lakes will dig southward through the OH valley today/Wed, cut-off over the TN Valley Thu/Fri as an expansive upper level ridge builds over the eastern 2/3 of the CONUS, then lift northward back to the Great Lakes Sat/Sun as the ridge breaks down in response to potent shortwave energy digging southeast from the Pacific NW to the Intermountain West/4-corners region. What remains of the ridge will shift downstream of the OH/TN valleys over the Mid-Atlantic/Carolinas early next week as additional shortwave energy moving ashore the Pacific NW digs SE through the Intermountain West, further amplifying a deep upper level trough over the Rockies. With the above in mind, expect slightly below normal temps Thu/Fri and lingering precipitation in assoc/w the cut-off upper low possible on Thu. A dry mid-upper level airmass wrapping around the southern periphery of the upper low will likely preclude any potential for precipitation on Fri. Dry conditions and near normal temperatures are expected to prevail for the remainder of the long term period, Sat/Sun as the upper low lifts north back to the Great Lakes and Mon/Tue as the aforementioned ridge aloft shifts eastward from the OH/TN valleys into the Mid-Atlantic/Carolinas. -Vincent
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&& .AVIATION /06Z TUESDAY THROUGH SATURDAY/... As of 156 AM Tuesday... A pre-frontal band of showers and thunderstorms over the NC Piedmont will move slowly eastward this morning and into the midday hours, diminishing/weakening along the way. IFR to MVFR ceilings through 12z should remain confined to KINT, KGSO, and KRDU, along the axis of stronger low-level moisture transport. These sub-VFR ceilings should gradually lift to VFR between 15 to 18z, with additional showers and storms re-developing across western NC and moving eastward this afternoon and evening as the sfc cold front stalls across western NC. Otherwise, at KFAY and KRWI, expect predominately VFR ceilings with some isolated shower or two possible. Looking beyond the 24 TAF Period: The combination of a quasi- stationary front across the Carolinas and a cut-off upper level low settling over the Tennessee Valley will keep unsettled weather in the form of scattered to numerous showers and storms through Thursday. Drier air from the west should gradually advect east into the area late Thursday and into Friday, leading to improving conditions with dry VFR conditions expected Friday and Saturday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...CBL NEAR TERM...CBL SHORT TERM...BS LONG TERM...Vincent AVIATION...30/BS is the U.S. government's official web portal to all federal, state and local government web resources and services.