When severe thunderstorms are moving through your area, that's a sign that you need to stay tuned to local radio broadcasts for watches and warnings related to the storm.  The potential for severe thunderstorms and/or tornadoes is forecast and categorized by the National Weather Service's Storm Prediction Center, which issues watches and warnings in conjunction with the Weather Service's local offices around the country.  If tornadoes are possible or imminent in your area, the National Weather Service will issue one or more watches and warnings. 

A tornado warning means that a tornado has been sighted by spotters or indicated on radar, and is occurring or imminent in the warning area. If a tornado warning is issued, people in the affected area are strongly encouraged to take cover immediately: MOVE TO AN INTERIOR ROOM ON THE LOWEST FLOOR OF A STURDY BUILDING. AVOID WINDOWS. IF IN A MOBILE HOME... A VEHICLE OR OUTDOORS... MOVE TO THE CLOSEST SUBSTANTIAL SHELTER AND PROTECT YOURSELF FROM FLYING DEBRIS.