SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1258 AM CDT Wed Aug 25 2021 Valid 251200Z - 261200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN PLAINS...UPPER MIDWEST AND SOUTHERN GREAT LAKES... ...SUMMARY... A few strong to severe thunderstorms with isolated wind damage may occur today from parts of the Upper Midwest into the southern Great Lakes. A hail threat may develop across parts of the northern Plains from this evening into tonight. ...Upper Midwest/Southern Greats... West to southwest mid-level flow will be in place today from the northern Plains into the Great Lakes. At the surface, a cold front will advance southeastward across the Upper Midwest, reaching the western Great Lakes by afternoon. A moist airmass, with lower to mid 70s F dewpoints, will be in place ahead of the front from the mid Missouri Valley east-northeastward into the southern and central Great Lakes region. Surface heating and enhanced low-level convergence along and ahead of the front, should result in isolated to scattered convective initiation this afternoon. The most favorable corridor for a marginal severe threat will likely be from eastern Iowa east-northeastward into Lower Michigan where the models develop strong instability. MLCAPE in the 3500 to 4500 J/kg range along with 20 to 30 kt of deep-layer shear should be enough for a marginal severe threat. The stronger multicells could be associated with an isolated wind-damage threat late this afternoon into early this evening. Large-scale ascent will be weak across Upper Midwest and Great Lakes region today. For this reason, confidence is low as to where the greatest severe potential will be. For this reason, will maintain a marginal risk for this update. ...Northern Plains... An upper-level ridge will be in place today across the southern and central Plains with flow remaining from the west-southwest in the northern Plains. At the surface, upslope flow will develop across much of the central and northern Plains as a trough develops in the lee of the Rockies. Warm advection will increase this evening across the northern Plains, as a low-level jet strengthens across the region. Lift associated with the jet will aid convective development. This combined with increasing instability aloft will make elevated thunderstorm likely across parts South Dakota this evening into tonight. Late evening NAM forecast soundings at Huron, South Dakota have MUCAPE reaching 4000 J/kg but also have a sharp low-level inversion. This would be favorable for elevated supercells with a threat for hail. The hail threat would likely be maximized during the late evening and early overnight period from western South Dakota to northwest Iowa. ...Eastern Georgia/South Carolina... A moist airmass will be in place today across much of the Southeast and Carolinas. Surface dewpoints in the lower to mid 70s F will result in the development of moderate to strong instability from central Georgia northeastward into central South Carolina. As surface temperatures warm, convection is expected to initiate along a sea breeze boundary. The boundary is forecast to move northwestward into eastern Georgia and central South Carolina this afternoon. Ahead of the boundary, MLCAPE is forecast to reach the 2500 to 3000 J/kg range by early afternoon with 0-3 km lapse rates in the 7.5 to 8.0 C/km. This could be enough for a marginal wind-damage threat with the stronger pulse storms. ..Broyles/Moore.. 08/25/2021 Read more LIVE: spc.noaa.gov
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