When a Tornado WATCH is issued by the 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.

When a Tornado WARNING has been issued by the 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.

More about Tornado Advice.