Thunderstorm warning:

A warning means that a severe thunderstorm has been detected by radar or a trained spotter. A warning is issued when the foul weather in question has begun happening. Be prepared for strong winds, heavy rain and hail.For severe thunderstorms, tornadoes and flash floods, a warning means the event is occurring.

Severe thunderstorms are larger than tornados, maybe 10 or 15 miles across. Still, their strong winds or large hail will hit only a small part of the area warned. For both types, a watch means you should keep up with the weather and be ready to act.