The Storm Prediction Center has issued a Severe Thunderstorm watch in effecy until 5am Saturda morning for the following counties, Black Hawk, Boone, Bremer, Butler, Calhoun, Carroll, Cerro Gordo, Crawford, Emmet, Franklin, Greene, Grundy, Hamilton, Hancock, Hardin, Humboldt, Kossuth, Marshall, Palo Alto, Pocahontas, Sac, Story, Tama, Webster, Winnebago, Worth, Wright, Buena Vista, Clay, Dickinson, Chickasaw, Floyd and Mitchell. Thunderstorms have begun to develop over west central Iowa and are moving to the east. Large hail and damaging winds will be the main threats.