Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 300602 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 202 AM EDT FRI SEP 30 2016 .SYNOPSIS... An upper level low stalled over the Tennessee valley will retrograde northward through the Ohio valley and lower Great Lakes this weekend. && .NEAR TERM /TODAY AND TONIGHT/... As of 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... The persistent upper low over the Tenn Valley will finally lift north into the Great Lakes and weaken, as a trough deepens over the Pacific Northwest. This will lead to a general trend toward higher heights over the eastern U.S, a surface high pressure ridge down the East Coast and temps near at or just slightly above. Before the low fully departs the region, some diurnal convection is possible across the far south/east Saturday and Sunday given the continued presence of the front that sinks over the area this weekend, but with diminishing in coverage with each day. Most of the long term focus is with the uncertainty in the track of what is currently Hurricane Matthew over in the Central Carribean. The official NHC track brings Matthew north across the Bahamas early next week in response to an upper trough cross the Gulf Coast region. This is still rather uncertain at day 7, however, and quite likely to change in the coming backs. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... As of 1245 AM Friday... 24-hr TAF period: IFR ceilings (500-1000 ft AGL) are expected to deteriorate to LIFR/VLIFR (100-500 ft AGL) between 06-09Z and persist through sunrise in association with low-level warm advection in advance of a cold front approaching from the west. Isolated convection could potentially affect all terminals through 12Z this morning, though probabilities are too low to warrant mention at most terminals (aside from perhaps INT/GSO). IFR/LIFR ceilings will begin to lift to MVFR everywhere late morning to early afternoon, then scatter out to VFR at the INT/GSO terminals by mid afternoon. MVFR ceilings will likely persist through the afternoon at eastern terminals, where isolated convection will also be possible. VFR conditions are expected at eastern terminals by or shortly after the end of the TAF period as a dry low-level airmass gradually advects eastward through central NC. Looking Ahead: Expect an extended period of dry/VFR conditions this weekend through early next week as a dry airmass prevails over the Carolinas. -Vincent && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Vincent NEAR TERM...Vincent SHORT TERM...Vincent LONG TERM...BS AVIATION...Vincent

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