 The National Weather Service in Des Moines has issued a severe thunderstorm warning for southern Black Hawk County in northeastern Iowa, northeastern Tama County in central Iowa, east central Grundy County in central Iowa, until 4.15 p.m. At 3.35 p.m., a severe thunderstorm was located 5 miles northwest of T.F. Clark State Park, or 14 miles southeast of Grundy Center, moving east at 30 miles per hour.