SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook CORR 1 NWS Storm Prediction Center Norman OK 1251 PM CDT Thu Apr 08 2021 Valid 091200Z - 101200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FRIDAY THROUGH FRIDAY NIGHT ACROSS PARTS OF SOUTHEASTERN OKLAHOMA...NORTHEASTERN TEXAS...SOUTHERN ARKANSAS...NORTHERN LOUISIANA...CENTRAL AND SOUTHERN MISSISSIPPI AND ADJACENT PORTIONS OF WESTERN ALABAMA... CORRECTED FOR TYPOS/WORDING ...SUMMARY... Severe thunderstorms are possible across parts of the southeastern Great Plains into the lower Mississippi Valley and central Gulf Coast States Friday through Friday night. This may include the development of one or two organized thunderstorm clusters, with the potential to produce swaths of damaging wind gusts. Large, damaging hail and a couple of tornadoes are also possible. ...Synopsis... A deep mid-level low is already in the process of migrating northeast of the lower Missouri Valley. This should continue through Friday and Friday night, as blocking remains prominent within the downstream flow, and another vigorous upstream short wave (emerging from the northern mid-latitude Pacific) continues inland, across the Rockies into the Plains. The lead impulse and associated surface cyclone are forecast to continue to weaken, while migrating across and northeast of the Upper Midwest and Great Lakes region by late Friday night. The cold front trailing the cyclone currently curves from the Upper Midwest through the lower Ohio and Mississippi Valleys, and is already becoming increasingly diffuse. As this continues, models suggest considerable boundary-layer moistening will occur into and through this period across a broad area of the southeastern Great Plains and lower Mississippi Valley. It appears that this will coincide with the northeastward advection of elevated mixed-layer air, on the southwestern periphery of the departing mid-level troughing, and ahead of a perturbation emerging from the southern mid-latitude or subtropical eastern Pacific. Models indicate that this southern perturbation will accelerate across Texas into the lower Mississippi Valley by late Friday night, within west-northwesterly to westerly flow in advance of the digging short wave of northern mid-latitude Pacific origin. It appears that associated forcing for ascent will contribute to new surface cyclogenesis across the southern Great Plains into the lower Mississippi Valley/Mid South vicinity by 12Z Saturday. ...Southeastern Great Plains into central Gulf States... While there appears reasonable model consensus on the general large-scale pattern evolution, considerable spread does exist concerning the synoptic and, particularly, the sub-synoptic developments for this period. Given moistening low-levels in the presence of steepening mid-level lapse rates, it does appear that substantial mixed-layer CAPE could develop Friday, in the presence of strong vertical shear. This provides support for the risk of severe storm development, though the extent and focus/details remain unclear at the present time. Based on the latest guidance, there does appear potential for the evolution of multiple clusters of severe storms Friday and Friday night, with isolated to widely scattered discrete supercell development also possible. There does appear a consistent signal in the model output that large-scale ascent along a strengthening mid-level baroclinic zone may provide support for increasing thunderstorm development across the Ark-La-Tex vicinity through southern Arkansas by mid day Friday. As the boundary-layer destabilizes, there appears potential for this activity to evolve into an intensifying and organizing mesoscale convective system, which will tend to advect/propagate eastward across the north central Mississippi/Alabama vicinity before weakening Friday evening. The approach of the southern mid-latitude/subtropical Pacific impulse may contribute to renewed thunderstorm development upstream, along the trailing convective outflow, by Friday evening. This may evolve into another organizing cluster of severe storms, which will probably tend to develop east-southeastward across the lower Mississippi Valley through early Saturday. Given the steep mid-level lapse rates, sizable CAPE and strong shear, stronger initial storm development may be accompanied by the risk for large, damaging hail, before activity grows upscale with damaging wind gusts becoming the more prominent hazard, along with the possibility of a few tornadoes. ..Kerr.. 04/08/2021
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