Hail in Butler County, Iowa

Public photos of tennis ball sized hail.

Warm air advection increased across the area through the day with a warm front draped across northern Iowa by the afternoon. Meanwhile a cold front was approaching Iowa from the northwest. Storms developed in the early evening in far southwest Iowa, moving across southern Iowa through late evening and overnight. Initial storms were surface based with CAPE exceeding 2000 J/kg and sweeping low level curvature in hodographs. Rotating updrafts supported hail growth with initial surface based storms resulting in a tornado in Union County. Storms became elevated overnight but remained strong, fueled by a strong 70+ knot low level jet. As storms in southern Iowa tapered off overnight additional storms developed along the boundary there. These storms became quite strong, producing golf ball to baseball sized hail from around 2 AM and lasting until after 5 AM.