Overview
- Watch 205, which began Friday at 5:15 PM CDT, covered western to northern Iowa, southern Minnesota, eastern Nebraska, and far southeast South Dakota through 1:00 AM with threats that included very large hail and a few tornadoes.
- Early in the evening, discrete supercells produced hail up to 2.5–3.5 inches before storms clustered, and a measured 74 mph gust was reported in southwest Iowa as bowing segments formed.
- SPC said the risk would shift toward widespread damaging winds as storms consolidated into a mesoscale convective system, with guidance supporting 70–80 mph gusts during the transition.
- At 10:30 PM, SPC issued Watch 207 for eastern Iowa, northern Illinois, and southern Wisconsin until 5:00 AM, expecting a west‑to‑east moving band with scattered damaging gusts to 70 mph and isolated large hail.
- Forecasters cited rich instability near 2,500 J/kg and strong wind shear to explain why hail‑producing supercells formed first, then a nighttime low‑level wind increase favored a faster line that boosts the straight‑line wind threat into Wisconsin and northern Illinois.