Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
414 ACUS02 KWNS 111730 SWODY2 SPC AC 111729 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1229 PM CDT Tue Jun 11 2024 Valid 121200Z - 131200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS IN THE UPPER MIDWEST... ...SUMMARY... Scattered severe thunderstorms capable of very large hail, damaging wind gusts, and a few tornadoes will be possible across parts of the Upper Midwest on Wednesday. The probable time frame for the most intense storms should be centered on late afternoon to early evening. ...Upper Midwest... A relatively complex convective scenario should unfold Wednesday with multiple rounds of severe potential anticipated. A mesoscale corridor of level 3-ENH risk may be warranted in later cycles, likely driven by greater hail probabilities, if spatial confidence increases. A fast largely zonal upper jet, initially along the international border over the Northwest, will spread into ND and northern MN by early Thursday. This will be coincident with a shortwave trough moving from the Canadian Rockies to the southern Prairie Provinces. A surface cyclone should track from southeast SK to along the MN/ON border by Wednesday evening. In advance of this wave, pronounced low-level warm theta-e advection will occur from the Great Plains amid an elevated mixed layer shifting east from the Dakotas and central High Plains. At least isolated elevated convection should be ongoing at 12Z along the periphery of the EML, centered on eastern SD into southwest MN. Consensus of guidance suggests this activity should persist into the diurnal heating cycle, centered on southern MN with a threat for isolated severe hail. Some of this activity may transition to surface-based character by midday to early afternoon with potential for an isolated strong wind threat as well. The spatial evolution of this early-day activity will likely modulate the overall threat, especially with northeast extent into western WI, where surface-based destabilization may be limited. The primary mid to late afternoon scenario should be focused ahead of the impinging cold front/surface trough in northwest MN to eastern SD. A confined plume of moderately large buoyancy should develop by peak heating with MLCAPE reaching 2000-3000 J/kg. The southwesterly low-level wind profile coupled with gradual veering to west-northwesterly (and strengthening) upper-level winds will favor hodograph elongation. Discrete supercells may tend to be more favored across northern MN initially before clustering into the evening. A messier convective mode is anticipated with southern extent, where residual outflow from early-day storms will likely focus regenerative convection. Tornado potential should be mesoscale-focused in this regime with enhanced low-level SRH near the trailing outflow, amid a more deeply mixed boundary layer to the west/south. This scenario should include embedded supercells within a southeast-sagging cluster into the evening as low-level winds become increasingly veered over IA. With greater buoyancy/instability to the west, the western portion of an evening cluster/MCS should contain the primary large hail/severe wind threat before convection wanes overnight. ..Grams.. 06/11/2024 $$