Tornado in Clay County, Iowa

A very brief tornado was observed in an open field around 3 miles southeast of Royal. The tornado was estimated to touch down around one-half mile southwest of the intersection of 420th Street and 170th Avenue. The tornado tracked east-northeast across open fields for around one minute before lifting south of 420th Street. There were no damage indicators present to derive a rating. The average path width was estimated at 20 yards based on video evidence.

An approaching mid-level disturbance broke a weak cap and allowed storms to erupt during the afternoon along a slow moving frontal boundary. These storms rapidly organized into short bowing segments and then became highly linear across northwest Iowa and southwest Minnesota during the evening. Initial supercell storms produced large hail with as much as 2000-3000 J/kg MLCAPE, but DCAPE of around 750-1000 J/kg allowed for the development of organized cold pools and an increasing wind threat. Several brief and highly visible tornadic spin-ups developed along the line of storms by late afternoon and evening across far eastern South Dakota, northwest Iowa and southwest Minnesota.

In addition, repeated thunderstorms brought as much as 2-4 inches of rain in a short period of time to portions of Plymouth and southern Sioux County in northwest Iowa. This same area had also received locally heavy rainfall during the previous days, resulting in spotty flooding of already saturated locations.