Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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609 FXUS62 KRAH 280710 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 310 AM EDT WED SEP 28 2016 .SYNOPSIS... A quasi-stationary frontal zone will meander over the area through late in the work week, as a deep upper level low settles over the Tennessee Valley. && .NEAR TERM /TODAY AND TONIGHT/...
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As of 310 AM Wednesday... As the mid/upper level cyclone drifts south towards the TN Valley, models indicate a weak surface wave will develop along the quasi-stationary frontal zone in place across Western NC. Daytime heating and result moderate destabilization within the seasonably moist PWATS 1.5-1.7" east of the frontal zone will support the re- development of showers and storm across the area this afternoon and evening, with increasing upper level diffluence and the arrival of better H5 height falls after 00z yielding the potential for convective regeneration and a south to north training band of convection overnight. Central NC remains in a marginal risk for severe storms this afternoon and evening, as the approach of the mid level speed maximum into the Southern Appalachians will increase 0-6km shear values of 30 to 40kts, highest north and west of the Triangle. If we indeed destabilize as strongly as the NAM suggest (2500- 3000J/Kg of MLCAPE), wouldn`t be surprise to see SPC upgrade the marginal risk to a slight risk as some of the stronger updrafts could exhibit rotation and bring the threat of wind damage, hail and isolated tornado. Storm intensity should decrease between 03 to 06z, as the BL cools/stabilizes from loss of heating. Additionally, as the mid/upper level flow becomes parallel to the southerly low-level inflow, convective training would bring the threat of heavy rainfall of 2 to 3 inches or higher with a threat of flash flooding in a few locations. With no airmass change, highs today will be very close to what we saw on Tuesday ranging from upper 70s north to mid 80s south. Lows65 to 70.
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As of 310 AM Wednesday... Will be issued shortly.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/... As of 355 PM Tuesday... A closed mid-upper low now over the Great Lakes will settle SWD and become increasingly separated/cut-off from the NRN stream flow across Canada, and ultimately reach the Lower OH/NRN TN Valley by early Thu. The models agree that the low will linger there through Fri, then lift NNEWD across the Great Lakes through the weekend. Meanwhile, a SRN stream jet will help carve a lingering trough axis across the SERN U.S. and ERN GOM, SWD to the vicinity of the Yucatan, during the same time. The ultimate placement and strength of this latter feature may play a role in the eventual track and strength of the tropical wave now several hundred miles E of Barbados. At the surface, a secondary cold front associated with the aforementioned closed low will have moved into the Appalachians by early Thu, then drift slowly EWD and merge, over central NC Thu afternoon, with the preceding frontal zone now stretching along the NC Blue Ridge. The front, and large-scale forcing and ERN fringe of colder temperatures/steep lapse rates accompanying the mid-upper low, will serve as a continued focus for a good chance of showers and storms on Thu. The merged frontal zone --and associated WRN bound of instability/convergence/chance of showers and storms-- will then pivot slowly NEWD through the NE Piedmont and Coastal Plain Thu night-Fri, before reaching and dissipating along the coast late Fri- Sat. A lee trough and associated light SLY flow will linger over the Carolinas this weekend, then yield to high pressure forecast to build across the NERN quarter of the CONUS, beneath NRN stream ridging aloft, through early-mid next week. Temperatures are expected to be near to slightly above average throughout the period. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... As of 125 AM Wednesday... Weakening area of thunderstorms across the Sandhills may impact KFAY over the next hour or two, where it could produce a strong thunderstorm wind gust of 30 to 35 mph and sub-VFR visibility restrictions in heavy rain. Otherwise, waning instability should lead to the dissipation of ongoing isolated to widely scattered convection across central NC. Moist low-level airmass in place east of frontal zone stalled over the NC mtns and foothills could lead to areas of stratus overnight, along with some patchy fog at KINT and KGSO where drier air aloft has allowed some partial clearing. Stratus should lift to VFR between 13 to 17z with re-development of showers and thunderstorms across the area this afternoon. 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. Conditions are expected to improve Friday through the weekend as drier air finally spreads in from the west. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...SMITH NEAR TERM...CBL SHORT TERM...SMITH LONG TERM...MWS AVIATION...CBL is the U.S. government's official web portal to all federal, state and local government web resources and services.