Forecasters often rely on massive computer programs called numerical weather prediction models to help them decide if atmospheric conditions will be right to support an environment in which tornadic storms might form. The models start with current weather observations and attempt to predict future weather using physics and dynamics to describe mathematically the atmosphere's behavior
Forecasters at the National Weather Service Storm Prediction Center (SPC) issue daily forecasts, or convective outlooks, for organized severe thunderstorms over the U.S. based on current weather observations and forecast models. They also closely monitor areas they think are at a higher risk for tornadoes.
If conditions develop that are favorable for tornadoes, SPC forecasters issue a severe thunderstorm or tornado watch that typically lasts four to six hours. Local forecast offices, emergency managers, storm spotters and the general public are alerted to the possibility of severe weather.
Tornado warnings are issued by the local National Weather Service Forecast Office when a tornado has been sighted or indicated by weather radar. People in the warning area should seek appropriate shelter immediately
