Environmental Health and Safety
Severe Weather Alert Terms
WATCH - 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.
WARNING - This term means the weather event (tornado, severe thunderstorm or flash flood) is imminent or is already occurring. Warnings usually are in effect for an hour or less. If a warning is issued for your area, be ready to take action immediately.
SEVERE THUNDERSTORM - Is a thunderstorm with damaging winds 58 mph or higher and/or large hail (3/4 inches in diameter or larger). If this term is in the forecast, you should pay extra attention to the weather and be prepared later for watches or warnings.
THUNDERSTORM - Is a rain shower accompanied by lightning and thunder. They frequently produce gusty winds, localized heavy rain and small hail.
TORNADO - Is a violently rotating column of air in contact with the ground that descends from the rain free base of a severe thunderstorm. They usually are funnel-shaped with the narrow end nearest the ground.
FUNNEL CLOUD - Is a violently rotating column of air that descends from the rain free base of a severe thunderstorm, but is not in contact with the ground. A tornado passes through the funnel cloud state during its development and dissipation.