Tornado watch:

A watch means that conditions are favorable for tornadoes to develop. A tornado watch is to alert people that tornadoes could form in an area within a certain time.

A watch is issued when there is a better than average chance that fouls weather may invade our area during a certain time frame. Indications for this may be a sudden change in barometric pressure, wind direction or other event. It is normally issued for 4 to 6 hours and includes many counties. Sometimes a severe tornado happens so quickly that warnings can't be issued in time.