Tornado watches mean that the present weather conditions are favorable for the formation of a tornado. Tornado warnings mean that tornado activity is imminent.
A watch is issued when conditions are favorable for severe weather conditions, for example, either for a severe thunderstorm or tornadoes. This doesn’t mean that severe weather is imminent. Typical watches will cover about 25,000 square miles. There are no set criteria for issuing watches. If the conditions seem consistent with a developing severe weather pattern, a watch can be issued. Watches can be changed and altered based on how the situation develops.
Warnings mean that severe weather is imminent. It is based on specific criteria and reports received by the National Weather Service.