SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0152 PM CST Thu Dec 24 2020 Valid 242000Z - 251200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE EASTERN CAROLINAS AND SOUTHEASTERN VIRGINIA... ...SUMMARY... Severe risk -- which includes potential for locally damaging winds and a few tornadoes -- continues across portions of the Carolinas and Mid-Atlantic region, and to a lesser degree southward into Florida. ...Discussion... Few changes appear necessary to the ongoing outlook at this time, as convection continues to evolve as expected. The primary change has been to remove the SLGT risk area centered over the Florida Panhandle, as the main convective band has now moved through the area of relatively greater CAPE. Though isolated severe risk will continue across Florida and southeastern Georgia, greater risk remains farther to the north across the eastern Carolinas and southeastern Virginia. Bands of pre-frontal convection will increase over the next few hours, with an associated uptick in severe/tornado potential expected. Later, a frontal band of convection is forecast to organize and shift eastward across this region, accompanied by risk for damaging winds and a tornado or two before moving offshore. ..Goss.. 12/24/2020 .PREV DISCUSSION... /ISSUED 1030 AM CST Thu Dec 24 2020/ ...Eastern/central Carolinas and Mid-Atlantic States... Multi-round severe convection is possible across parts of the region this afternoon into tonight, particularly for the eastern Carolinas/southeast Virginia, where semi-discrete warm sector storms this afternoon/early evening could be followed by a well-organized convective line late this evening and early in the overnight. Multi-layer cloud cover remains prevalent at midday across the region with air mass modification occurring near the coastal Carolinas where low/middle 60s F surface dewpoints are becoming more prevalent. North/northeastward-racing bands of convection over the eastern Carolinas will persist through the afternoon where the convection should gradually intensify as it becomes rooted within the increasingly moist/unstable boundary layer, although the persistent cloud cover and the possibility of a lingering warm layer aloft leads to some temporal uncertainty. Regardless, extremely strong low-level/deep-layer shear, accentuated by 55-60 kt in the lowest 1 km AGL and 300+ 0-1 km SRH, will be supportive of fast-moving supercells capable of a tornado/damaging wind risk, particularly late this afternoon through early evening. Given the magnitude of the vertical shear/SRH, a strong tornado cannot be ruled out. Otherwise, as previously mentioned, an additional round of regional severe risk will likely occur this evening into the overnight as a strongly forced convective line evolves and spreads east-northeastward across the Carolinas and coastal Mid-Atlantic/Delmarva. Damaging winds are the most probable severe hazard, although a QLCS-related tornado risk may exist as well. ...Florida/Georgia... A northeast/southwest-oriented composite convective line across southern Georgia/Florida Panhandle at late morning immediately precedes an eastward-moving cold front. Some additional moistening/diurnal destabilization will occur across the Florida Peninsula into far southern Georgia ahead of the front/convective line, with surface-based destabilization otherwise remaining minimal farther north into central/eastern Georgia. Low-level/deep-layer winds will further strengthen across the region, although low-level winds will tend to slowly veer with wind profiles trending more unidirectional over time. Even with relatively modest buoyancy, this scenario will support further organization and development of upscale-growing quasi-linear convective bands this afternoon. An isolated damaging wind/tornado risk will exist across the region through the afternoon, with the overall severe risk shifting eastward/tending to diminish toward and after sunset.
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