A Tornado Watch means that the weather conditions outside are starting to come together for the development of thunderstorms that could produce a tornado. It takes specific conditions to produce tornadic thunderstorms, and many times the watch might be issued but tornadic thunderstorms will not develop.
A tornado watch does not mean that tornadoes are forming. A tornado watch is issued for a long period of time, usually 4 hours or more, and it is issued for a large area of a state or several states. A tornado watch is not issued by any local television station or a local National Weather Service office. A tornado watch is issued by the Storm Prediction Center in Norman, Oklahoma.