Hail in Union County, Iowa

Trained spotter reported nickel sized hail on Highway 34 east of Creston.

An omega block pattern set up in mid September and on the 16th Iowa was just west of the ridge axis. This resulted in a hot and humid period and MLCAPE was around 2000-3000 J/kg. The 0-6 km shear was weak under the ridge at under 20 kts. In the deeply unstable environment, pulse thunderstorms were able to develop quickly but the lack of shear prevented better organization and the storms would eventually collapse on themselves. This resulted in widespread scattered thunderstorms across Iowa that produced quarter sized hail and then collapsed and produced wind gusts of 50-60 mph. The lack of flow also meant that storm motions were around 5-10 mph. In an environment with precipitable water over 1.5 inches and deep warm cloud layers allowing for efficient rain production, the slow storm motions resulted in areas with 4-6 inches of rain. Even so, dry antecedent conditions prevent widespread hydrologic problems. Flash flooding was reported in Fort Dodge when thunderstorm set up over the town, resulting in closed roads and stalled vehicles across town. Storms diminished in strength overnight but remained efficient rain producers into the early morning of September 17th.