Northeast Iowa-Wisconsin Supercells Gear Up for EF2+ Tornadoes, Tennis Ball Hail — SevereWX

Imminent supercell development across Northeast Iowa into northwest and north-central Wisconsin poses a serious severe weather threat this late afternoon and evening.

The Storm Prediction Center has issued Mesoscale Discussion 1674, highlighting a 95% chance of a tornado watch as storms fire along a cold front in the Upper Mississippi Valley. A very moist airmass, combined with lift from a northern Minnesota shortwave trough, will overcome surface-based capping, sparking supercells amid 50-60 kt effective shear.

Key threats include:

• Strong tornadoes: Most probable peak intensity of 120-145 mph (low-end EF2 to EF3), favored with supercellular structures.
• Very large hail: 1.50-2.50 inches (golf ball to tennis ball size) due to steep mid-level lapse rates.
• Damaging winds: Gusts to 65-80 mph, potentially exceeding 75 mph where storms grow upscale.

Timing remains the biggest uncertainty, but expect initiation by late afternoon (around 4-5 PM CDT), with peak activity through 9 PM CDT. Mid-level storms from southern Minnesota are influencing the setup near earlier outflow boundaries, enhancing storm potential near the front.

This corridor spans from Dubuque to Madison vicinities—stay vigilant as a tornado watch could drop soon. SPC graphics available at spc.noaa.gov.

Preparedness reminder: Know your safe spot, monitor local NWS updates via NOAA Weather Radio or apps, and have a severe weather plan ready. Act quickly if warnings issue.