People moving into areas where tornadoes are common may hear the term "tornado watch" without knowing exactly what it means. A tornado watch means that weather conditions in and around the watch area are going to deteriorate and tornado activity is possible. The Storms Prediction Center in Norman, Oklahoma issues tornado watches. The center analyzes conditions in storm-prone areas and determines whether tornado activity is likely. A watch is then issued.
A tornado watch is defined in a rectangular area, sometimes covering hundreds of square miles. The tornado watch is usually of several hours' duration and is issued some time before severe weather is expected in the area. The advance issuance is designed to warn people that bad weather is approaching and give them time to review safety precautions and take action to keep themselves safe.
A tornado watch is not the same kind of advisory as a tornado warning. A warning is issued by the local National Weather Service office and means that a funnel cloud has either been sighted by a trained spotter or is indicated on radar. Tornado warnings are issued for specific areas of one county at a time. During a tornado warning, the emergency management agency of the county sounds tornado sirens in the affected areas.
Even if the sun is shining when a tornado watch is issued, a person should take the advisory very seriously. A tornado warning may never be issued, but it's a good bet that severe thunderstorms will move through the area, and these carry high winds, cloud-to-ground lightning and sometimes hail. Straight-line winds are also a risk with severe thunderstorms.
Those who live in tornado-prone areas usually have NOAA weather radios that sound an alarm when their county goes under a tornado watch or warning. These are especially important at night, since sirens may not be audible over high winds, but the alarm is sufficiently loud to wake even a sound sleeper. A tornado watch should always mandate action, even if it is just to monitor weather conditions. Doing so may save a life.