Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 301811 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 210 PM EDT FRI SEP 30 2016 .SYNOPSIS... A weak wave of low pressure and associated frontal zone will drift east across our region through early Saturday, then offshore through the rest of the weekend, while a persistent upper level low over the Tennessee Valley lifts across the Lower Great Lakes. && .NEAR TERM /TODAY AND TONIGHT/... As of 1000 AM Friday... Storm chances were increased and expanded a couple of hours ago to account for broken convective band curving from SW VA to Raleigh to Clinton to Wilmington, with elements tracking roughly northward. The latest surface analysis shows the surface low over the NC Foothills with a cold/occluded front extending down through western and southern SC and a warm/stationary front extending eastward across northern NC. Already a few strong to severe storms have formed in this band within a somewhat favorable environment of good deep layer shear (45-55 kts), strong mid level jet streak (55-60 kts), and marginal instability (~1000 J/kg of MUCAPE), although dynamic forcing for ascent is largely to our west, closer to the influence of the vortex centered over the KY/IN border. Will continue to monitor the severe threat over the next several hours as the mid level speed max tracks up the east side of the vortex, with the surface cold/occluded front easing slowly toward the ENE. Will keep good chance to likely pops in the Triangle to the north and east, with lower slight-chance to low chance pops over the SW CWA. Highs still expected to be in the upper 70s to lower 80s. -GIH Earlier discussion from 200 am Friday: Strong low-level warm advection in advance of a cold front extending southward along the I- 77 corridor and upper level forcing in the form of a jet entrance/exit and small amplitude waves/weak DPVA/ rotating around the eastern periphery of a stalled upper level low in Kentucky have allowed deep convection to develop within the dry mid/upper level airmass in place over central/western NC since 00Z. Nocturnal destabilization assoc/w low-level warm advection will yield 1000- 2000 J/Kg of MUCAPE through sunrise. Low-level FGEN and upper level forcing on the eastern periphery of the stalled upper low may further enhance thermodynamics via the release of potential instability, in the presence of vertical wind shear sufficient for supercells (SCP values 2-6). Any isolated convection in central NC this morning should remain elevated in nature, with parcels launching from ~925 mb (atop a ~2500 ft stable layer). With the above in mind, isolated convection will remain possible overnight, primarily in the NW Piedmont where low-level forcing will be juxtaposed with marginal upper level forcing on the eastern periphery of the stalled upper low. If layer-lifting is sufficient for deep convection to survive entrainment of dry air aloft in the NW Piedmont, updrafts could acquire mid-level rotation and exhibit deviant motion. Given the elevated nature of any convection and the lack of such characteristics thus far, severe weather appears unlikely. Should a robust elevated updraft acquire rotation, small to marginally severe hail could not be ruled out. Instability will decrease from west-east today as a drier low-level airmass advects into portions of the area (western Piedmont for sure) attendant a slow moving cold front and temps aloft (H5) begin to warm. The front is expected to further slow down this afternoon, stalling in a NW-SE orientation along/near a line from INT-TTA-CTZ. As a result, expect dry conditions in the SW Piedmont with isold/sct convection possible elsewhere and the relative best chances from in the NE Coastal Plain. Expect highs ranging from near 80F in the N/NW Piedmont to ~85F in the Sandhills and SE Coastal Plain. Lows tonight ranging from the mid 50s west to mid 60s east. If convection can survive entrainment of dry air in the mid/upper levels this afternoon, instability/shear would support supercellular organization along with a potential for damaging winds/large hail. Though diurnal destabilization will be greatest across portions of the the Sandhills/SE Coastal Plain, the potential for an isolated severe storm may be confined to the N/NW Piedmont in closer vicinity to the stalled upper low where upper level forcing /layer-lifting/ (and release of potential instability) is more likely. -Vincent && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... As of 200 AM Friday... Dry/stable conditions will prevail sat/sat night as a dry low-level airmass advects into the region beneath an increasingly warm/dry mid- level airmass as the upper level low retrogrades northward away from the region (toward the Great Lakes). Expect highs in the upper 70s to lower 80s and lows mid/upper 50s to lower 60s. -Vincent && .LONG TERM /SATURDAY THROUGH THURSDAY/... As of 350 PM Thursday... he upper low over the Great Lakes will finally open up and weaken as it finally ejects eastward off the New England Coast late Monday and into Tuesday. Warm dry air aloft will cap Central NC off from any convection Sunday and Monday with daytime highs continuing to run a good 3 to 5 degrees above normal. Highs in the upper 70s north to lower 80s south. Lows 60 to 65. In the wake of the low lingering off the New England Coast, Canadian high pressure will wedge south down the Atlantic Seaboard, bringing cooler, more seasonable temperatures Tuesday through Thursday. The NHC forecasts has Matthew moving northward through the Bahamas on Tuesday, with large model spread thereafter in both the track and speed of Matthew for the latter half of next week. Refer to the National Hurricane Center for the latest information on TC Matthew. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
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As of 210 PM Friday... MVFR cigs persist at RDU/RWI/FAY with a continued threat for scattered showers and isolated storms, while conditions have improved to VFR at INT/GSO as a slow moving cold front has shifted just east of these locations, with drier air moving in. The dominant MVFR conditions at RDU/RWI/FAY will improve to VFR from late afternoon through early to mid evening as dry air gradually works in from the WSW, with a corresponding end to the shower/storm chances. There is a small chance of MVFR or IFR vsbys in fog at RWI/RDU early Sat morning but chances appear too remote at this time to include in the terminal forecasts. VFR conditions are expected at all sites late tonight through Sat as high pressure builds in from the WSW. Surface winds from the SE at 6-12 kts will become light/variable for much of tonight before becoming southwesterly Sat behind the front. Looking beyond 18z Sat: VFR conditions are likely to dominate through Wed, although a period of sub-VFR fog/stratus is possible areawide early Wed morning. -GIH
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...Hartfield/Vincent SHORT TERM...Vincent LONG TERM...CBL AVIATION...Hartfield

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