They usually are preceded by very heavy rains or hail. The National Weather Service uses specific terminology for severe weather forecasts. This term, when used with the words tornado or severe thunderstorm, means that tornadoes or severe thunderstorms are possible in the mentioned area. Watches are usually in effect for several hours and indicate that atmospheric conditions are favorable for these storms to develop. Tornadoes or severe thunderstorms need not be present for a watch to be issued.
Warnings usually are in effect for an hour or less.
If a warning is issued for your area, be ready to take action immediately. If this term is in the forecast, you should pay extra attention to the weather and be prepared later for watches or warnings. They frequently produce gusty winds, localized heavy rain and small hail. They usually are funnel-shaped with the narrow end nearest the ground. A tornado passes through the funnel cloud state during its development and dissipation.