When a Tornado WATCH is issued by the National Weather Service, you are advised to take precautions.  A tornado watch means that conditions are favorable for a severe thunderstorm or a tornado to occur. It does not mean that they will occur. It only means they are possible. You should keep an eye on the weather and remain alert for approaching storms. You may continue with your normal activities, but be prepared to take action should a tornado develop.

When a Tornado WARNING is issued by the National Weather Service, you are advised to take action, immediately! A tornado warning means that a tornado has been sighted or indicated by local weather radar. There is imminent danger to life and property. Seek safe shelter immediately.

More about Tornado Advice.