Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
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243 ACUS01 KWNS 050600 SWODY1 SPC AC 050559 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1259 AM CDT Sat Oct 05 2024 Valid 051200Z - 061200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF NORTHERN WISCONSIN AND ADJACENT PORTIONS OF SOUTHERN UPPER MICHIGAN... ...SUMMARY... Isolated strong to severe thunderstorms may produce hail and gusty winds across parts of northern Wisconsin into the Upper Peninsula of Michigan this evening. ...Synopsis... Flow aloft will remain generally weak over the southern half of the U.S. today, where upper ridging will prevail. This ridging will -- however -- be interrupted by an elongated/weak trough comprised of several smaller-scale vorticity maxima, extending from the southeastern states west-southwestward across the Gulf of Mexico to northern Mexico. Farther north, a faster belt of westerly flow will prevail, with an embedded/potent short-wave trough forecast to move across the northern Plains through the day, and then the Upper Mississippi Valley/Upper Great Lakes region overnight. Accompanying the upper trough, a surface low is forecast to advance east-northeastward across the Canadian Prairie, and into northwestern Ontario through latter stages of the period. A trailing cold front will shift eastward across the north-central U.S. and southward across the Plains -- reaching a position from Lower Michigan southwestward to the Ozarks, and then west-southwestward across Oklahoma to Far West Texas by Sunday morning. ...Central and northern Wisconsin north to Lake Michigan... As a cold front advances across the Upper Midwest area through the afternoon, a capped boundary layer should hinder convective development. As the boundary crosses the Upper Mississippi Valley around sunset, and the upper system advances, the combination of strong ascent and steepening lapse rates aloft should permit eventual development of showers and scattered thunderstorms. With a rather dry -- and nocturnally stabilizing -- boundary layer expected ahead of the front, convection should evolve within a slightly elevated but amply unstable layer. Strong southwesterly flow aloft will provide sufficient shear for organized/rotating storms -- and thus risk for hail is evident. Additionally, the strongly dynamic upper system/strong mass response suggests potential for downward transport of strong flow aloft -- potentially manifesting as severe-caliber wind gusts at the surface. Given the overall severe risk, will introduce a small SLGT/level 2 risk across this area, with the primary risk expected to be hail. However, potential for strong/gusty surface winds may also -- depending upon boundary-layer evolution -- warrant upgrade to 15% probability in later outlooks. ..Goss/Squitieri.. 10/05/2024 $$