Northeast Iowa, Wisconsin Supercells Set to Unleash EF2-EF3 Tornadoes, Tennis-Ball Hail — SevereWX

Supercells are priming to fire late this afternoon across northeast Iowa into northwest and north-central Wisconsin, packing a punch of all severe hazards including some significant ones.

The SPC's Mesoscale Discussion 1674 highlights a very moist airmass ahead of a cold front in the Upper Mississippi Valley, where a capping inversion has delayed development so far. Cumulus fields along the front remain flat-topped, but lift from a shortwave trough in northern Minnesota is overspreading the region. Combined with continued daytime heating and outflow from earlier storms near La Crosse and Davenport, expect vertical development by late afternoon—most likely near the cold front and outflow intersection.

Key Threats:

• Tornadoes: Strong shear (50-60 kt effective) favors supercell structures, with peak intensities of 120-145 mph (EF2 to low EF3).
• Hail: Steep mid-level lapse rates support large to very-large hail, peaking at 1.50-2.50 inches (golf ball to tennis ball).
• Winds: Gusts to 65-80 mph, potentially higher as storms grow upscale.

Timing and exact initiation location remain the biggest uncertainties, but the SPC pegs tornado watch odds at 95% through 2100Z (4 PM-9 PM CDT). Affected WFOs include MPX, ARX, DLH, MKX, GRB, and MQT.

Check the SPC graphic for the precise lat/lon box. This setup screams high-end discrete storm mode before any upscale growth.

Stay Prepared: Monitor radar closely, have multiple alert sources, secure outdoors, and know your safe spot if warnings issue. Severe weather can change quickly—don't wait for the watch.