Governor Vilsack has declared this “Severe Weather Awareness Week” in Iowa. Weather officials are highlighting a different area of severe weather each day to prepare people for the upcoming spring and summer weather. Today’s topic is thunderstorms and Jeff Wallenfang, a meteorologist at the National Weather Service office in metro Des Moines, describes the criteria for a thunderstorm to be considered “severe.” He says there needs to be a 58-mile an hour win, penny-sized hail or a tornado.Wallenfang says severe thunderstorms can take place any time of year, the most active months are April through June.Other topics being covered this week include NOAA weather radio, tornadoes, flooding, and severe weather preparedness. A statewide tornado drill will be held Wednesday morning.