Lighting from an approaching thunderstorm fills the sky at Ellsworth Air Force Base, S.D., June 9, 2012. Thunderstorms, usually associated with severe winds, occur on average once every 45 days during the summer months. Airmen and their families should be prepared for all types of inclement weather and know the location of the nearest emergency shelter. (U.S. Air Force photo by Airman 1st Class Zachary Hada/Released)