A tornado warning is issued by the local National Weather Service (NWS) office whenever a tornado has been sighted or NWS Doppler Radar indicates a thunderstorm capable of producing a tornado. A severe thunderstorm warning is issued whenever a severe thunderstorm is observed or NWS Doppler Radar indicates a thunderstorm capable of producing damaging winds or large hail. Warnings are for smaller areas, such as counties, and are usually 30 minutes to one hour in length. You must act immediately when you first hear the warning. If severe weather is reported near you, seek shelter immediately. If not, keep a constant lookout for severe weather and stay near a shelter.