Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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169 FXUS62 KRAH 270758 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 358 AM EDT TUE SEP 27 2016 .SYNOPSIS... A cold front will move into the Carolinas today and will become quasi-stationary over the area through late in the work week, bringing unsettled weather through the period. && .NEAR TERM /THROUGH TONIGHT/... As of 330 AM Tuesday Deep mid/upper level cyclone over Southern Ontario and the Upper Great Lakes will drop south into the Ohio Valley this evening and overnight. Attendant cold front has made its way into eastward into the Southern Appalachians this morning, but will move very little over the next 2 to 3 days, becoming quasi-stationary across the Western Carolinas through Wednesday night as the cyclone is forecast to cut off from the westerlies and drift farther south towards the TN Valley/Southern Appalachians. A pre-frontal band of convection over the NC Piedmont that developed within a swath of strong low- level moisture convergence in advance of the cold front coming into the mountains has made little progress eastward, diminishing/weakening along the eastern flanks as it attempts to move into the Central Piedmont. Rainfall rates and amounts have significantly decrease within this convective band, ending any flooding concerns. Will see a chance of some lingering light rain showers across the Triangle for the morning commute before further waning as the showers move east into coastal plain. Expect a midday to early afternoon lull before weak to moderate destabilization, maximized across western NC along the zone of strongest moisture convergence, is expected to lead to the re- development of scattered to numerous showers and some storms by mid afternoon and continuing into the evening and overnight hours as the front settles in the lee of the mountains. The threat for severe storms will be limited by weak mid-level lapse rates and cloud cover, but cannot rule out an isolated severe storm if moderate instability develops as proposed by the NAM. But still think the primary threat will be localized heavy rain and isolated flooding given high PWAT airmass of 1.6-1.8". Highs in the mid to upper 70s north to lower/mid 80s south. Lows tonight 65 to 70. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
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As of 358 AM Tuesday... As the mid/upper level cyclone drifts south into the TN Valley, models indicate a weak surface wave will develop along the quasi- stationary frontal zone in place across Western NC. Enhanced low- level moisture convergence coupled with strengthening vertical lift from the associated height falls and mid/upper level speed max spreading east into the area late in the day and into the overnight hours may lead to the "wettest" period and potentially greatest heavy rain/flooding threat. The strengthening mid-level flow also results in improved shear parameters to 30 to 35kts, so cannot rule out an isolated severe storm Wednesday afternoon. Highs again in the mid 70 north to lower 80s southeast. Lows in the 60s.
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&& .LONG TERM /THURSDAY THROUGH TUESDAY/... 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 && .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...CBL LONG TERM...Vincent AVIATION...CBL is the U.S. government's official web portal to all federal, state and local government web resources and services.