The Storm Prediction Center has issued a Severe Thunderstorm Watch effective until 1am for the following counties, Adair, Adams, Audubon, Benton, Black Hawk, Boone, Bremer, Buchanan, Butler, Calhoun, Carroll, Cass, Cerro Gordo, Chickasaw, Clarke, Crawford, Dallas, Decatur, Fayette, Floyd, Franklin, Fremont, Greene, Grundy, Guthrie, Hamilton, Hancock, Hardin, Howard, Humboldt, Jasper, Lucas, Madison, Marion, Marshall, Mills, Mitchell, Montgomery, Page, Pocahontas, Polk, Pottawattamie, Poweshiek, Ringgold, Sac, Shelby, Story, Tama, Taylor, Union, Warren, Webster, Winneshiek, Worth and Wright.

Thunderstorms have developed and have become severe. The main threats will be from large hail and damaging winds. There will be some locally heavy rainfall as well, but flash flooding is not likely.