Large Hail and Damaging Winds Likely Across Upper MS Valley; Late Afternoon; August 29th, 2024

Photo byNational Weather Force

Brief Outlook:

Scattered severe thunderstorms are expected across the Upper Mississippi Valley tomorrow, particularly impacting areas in southeastern Minnesota, western Wisconsin, and northeastern Iowa. Main Impact: Damaging winds, large hail, and isolated tornadoes.

Region Impacted: Southeastern Minnesota, Western Wisconsin, and Iowa

Upper-Level Dynamics/Forecast:

A mid-level shortwave trough will traverse the northern Plains, bringing an increased risk of severe thunderstorms to the Upper Mississippi Valley. The trough will enhance mid-level westerly winds, expected to reach 40-50 knots, contributing to storm organization. Additionally, a strong upper-level jet streak will provide sufficient lift, creating an environment conducive to supercells and organized storm clusters.

Surface Forecast Conditions:

At the surface, instability values are expected to reach very high numbers 3000-4500 J/kg some areas even higher, driven by hot temperatures and ample moisture with dewpoints in the upper 60s to low 70s. Also, Steep mid-level lapse rates will further enhance the potential for these storms to mature. A cold front moving southeastward through the region will serve as a focal point for thunderstorm initiation becoming severe quickly. Effective shear will support the development of discrete supercells, capable of producing large hail and isolated tornadoes. As the evening progresses, these storms may evolve into larger clusters or lines most likely becoming a squall line, with damaging winds becoming the primary threat sometimes in excess of over 70mph wind gusts at times.

Timing:

Storms are expected to initiate by mid to late afternoon after the cap weakens ahead of the cold front (around 2-4 PM CDT) in southeastern Minnesota and northwestern Iowa, with activity spreading into western Wisconsin by early evening/late evening as a long squall line is expected to form and move eastward with time. Peak intensity is likely to occur from late afternoon through the evening and continuing into the overnight hours as it pushes east, with the strongest storms expected during this period. The storms are likely to weaken gradually overnight as they move eastward.

Main Impact: damaging winds, large hail, isolated tornadoes and lightning.

Stay tuned for more updates.

Sina⚡⚡

Co-Owner/CTO and Lead Forecaster of NWF Innovations & NWF Networks

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