Tornado in Calhoun County, Iowa

Tornado developed east of Pomeroy and moved north passing into Pocahontas county shortly after forming. The tornado remained in open fields in Calhoun county and did not impact any damage indicators, hence the EFU rating for this portion of the path.

Convection percolated along a warm front across the area through the morning. By afternoon, storms re-strengthened as as daytime heating helped enhance instability. Despite good instability with MLCAPE over nearing 2000 J/kg, lapse rates were modest and speed shear was weak. Despite this, directional shear was good and when combined with instability for brief stretching, allowed for a number of weak and short-lived tornadoes to develop. While 13 tornadoes occurred, they were confined to two small areas in Iowa where storms trained, resulting in several storms over the same locations. In addition, the training storms made for pockets of heavy rain with three to four inches or more of rain. This did result in flash flooding in Pocahontas County with impacts to homes and businesses.