Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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103 FXUS62 KRAH 291814 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 215 PM EDT THU SEP 29 2016 .SYNOPSIS...
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A large upper level low will hold over Kentucky and southern Indiana through Friday, as a surface front holds along the North Carolina Foothills. The upper low will weaken and drift north and northeastward over lower Michigan through the weekend, as the surface front pushes slowly eastward across central North Carolina.
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&& .NEAR TERM /TODAY AND TONIGHT/... As of 1145 AM Thursday... Have issued a flash flood watch for far eastern and southeast sections of the forecast area through 10 pm this evening, although much of this area is under ongoing flood warnings or advisories anyway. A large area of 6-10" accumulations since yesterday afternoon has led to significant flooding over portions of the Sandhills and central/southern Coastal Plain. Additional convection is a near certainty this afternoon, with nearly band-parallel cell motions suggesting additional 1-3" are possible with locally higher totals not out of the question, all of which would most certainly exacerbate ongoing flooding. Next up is the potential severe threat for much of the CWA. The 12z GSO sounding showed minor elevated instability which would be fully released with heating, some of which is taking place this morning with holes in the clouds introducing enough insolation to push low level lapse rates up to 6+ C/km, with diminishing CINH. Deep layer effective shear is more than sufficient at 40-50 kts, and projected MUCAPE of 1500-3000 J/kg this afternoon added to the large scale lift generated by upper divergence and DPVA around the large vortex over KY should prompt strong to severe storm development by early to mid afternoon. Little to no change to highs today, upper 70s to lower 80s. -GIH Earlier discussion from 445 am... A busy midnight shift here in central NC, one which began with a severe thunderstorm watch and transitioned into a 100-year rainfall event (ongoing at ~09Z) across portions of the Sandhills (i.e. Hoke/Cumberland/Harnett counties) where as much as 5-8" of rain has fallen over the past 8-12 hours. As such, the forecast discussion this morning will be brief. Several SW-NE oriented lines of convection developed over central NC yesterday afternoon/evening in assoc/w moderate diurnal destabilization, low-level convergence attendant a pre-frontal trough, and diffluent flow aloft downstream of a potent upper level low. During the overnight period, rich low-level moisture assoc/w southerly flow in advance of the approaching cold front has maintained sufficient nocturnal instability for convection to persist, resulting in significant rainfall and /potentially life- threatening/ flooding across portions of Harnett, Hoke and Cumberland counties this morning. Although the cold front may make some slow eastward progress into the area today, the parent upper level low will cut-off /stall/ over the TN valley this aft/eve, and additional eastward progress of the front is unlikely thereafter. As a result, expect a good chance of convection again this aft/eve into tonight. A few severe storms cannot be ruled out, and an isolated flash flood potential will persist. -Vincent && .SHORT TERM /FRIDAY AND FRIDAY NIGHT/... As of 445 AM Thursday... On Friday, expect conditions similar to Thursday with the upper level low stalled over the Cumberland Plateau and the attendant cold front stalled over central NC. -Vincent && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 440 AM Thursday... Stubborn upper level low over the Southern Ohio valley will lift slowly north, back over the Great Lakes through the weekend. At the surface, the lingering orphaned surface front will dissipate across the area. With Central NC on the eastern periphery of the deep cyclonic flow and the back-edge of the deeper moisture plume (PWATS ~1.5")lingering over the coastal plain of NC, we`ll continue to see a threat of mainly diurnal isolated to widely scattered showers Saturday and Sunday, diminishing in coverage with each passing day. Temperatures will continue to run slightly above normal with highs ranging from upper 70s north to lower 80s south. The closed low over the Great Lakes will finally open up and weaken as it finally ejects eastward, moving off the New England Coast Monday and into Tuesday. In it`s wake, sfc high pressure building east and south down the Atlantic Seaboard will bring cooler, more seasonable temperatures to the area by Tuesday/Wednesday. Large uncertainty looms for the latter half of the upcoming work week with respect to Tropical Storm Matthew. The NHC official forecast has Matthew near Eastern Cuba Monday evening, with questions as to whether Matthew will get picked up and directed northward by an upper level trough over the Gulf of Mexico. Stay tune and check with the National Hurricane Center for the latest on Matthew. Users are reminded that the average NHC track errors at days 4 and 5 are on the order of 180 and 240 miles, respectively. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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As of 215 PM Thursday... Conditions have improved to VFR over all but FAY, where MVFR cigs lingered, and near GSO where MVFR cigs returned with showers in the vicinity. Periods of sub-VFR conditions -- mainly MVFR but briefly IFR at times -- is expected at all central NC terminal sites through the rest of the afternoon, as scattered to numerous showers and storms form over the area and move swiftly toward the north, generating brief heavy rain, periodic wind gusts, and possible small hail. The shower/storm coverage will slowly decrease through the evening and night from SW to NE, with RWI the last to see the rain threat diminish. With a moist ground and light winds from the SE, widespread IFR to LIFR cigs and MVFR to IFR vsbys are expected to develop at all sites after 07z tonight, lasting until around 13z Fri. VFR conditions expected after that, through the end of the TAF valid period. A few showers may linger through the morning in the east near FAY/RWI. Looking beyond 18z Fri, another round of MVFR showers and isolated storms are expected mainly at RDU/FAY/RWI Fri afternoon into early evening as a surface front shifts slowly eastward into central NC. This front will weaken and dissipate heading into the weekend, allowing the better rain chances to shift to our east. Except for a potential for MVFR or IFR fog/stratus at RWI early Sat morning, VFR conditions will dominate through Tue with low rain chances. -GIH
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&& .RAH WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch until 10 PM EDT this evening for NCZ028-042-043- 075>078-084>086-088-089. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield/Vincent SHORT TERM...Vincent LONG TERM...CBL AVIATION...Hartfield

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