According to the National Weather Service, here are the differences between a Tornado Watch, Tornado Warning, and Tornado Emergency:
Tornado Watch: Be Prepared! Tornadoes are possible in and near the watch area. Review and discuss your emergency plans, take inventory of your supplies and check your safe room. Be ready to act quickly if a warning is issued or you suspect a tornado is approaching. Acting early helps to save lives! Watches are issued by the Storm Prediction Center for counties where tornadoes may occur. The watch area is typically large, covering numerous counties or even states.
Tornado Warning: Take Action! A tornado has been sighted or indicated by weather radar. There is imminent danger to life and property. Move to an interior room on the lowest floor of a sturdy building. Avoid windows. If in a mobile home, a vehicle, or outdoors, move to the closest substantial shelter and protect yourself from flying debris. Warnings are issued by your local forecast office. Warnings typically encompass a much smaller area (around the size of a city or small county) that may be impacted by a tornado identified by a forecaster on radar or by a trained spotter/law enforcement who is watching the storm.
Tornado Emergency: Seek Shelter Immediately! A tornado emergency is the National Weather Service’s highest alert level. It is issued when a violent tornado has touched down in the watch area. There is a severe threat to human life and property, with catastrophic damage confirmed. Immediately seek refuge in the safest location possible. Call friends and family who are within the watch area to ensure they are aware of the situation. If you see a tornado approaching, do not attempt to outrun it in a vehicle; shelter in place. Once safe, be sure to monitor your local forecast for the latest updates.1
1925 Tri-State Tornado
The deadliest tornado in United States history happened on March 18, 1925 (100 years ago). The 1925 Tri-State Tornado touched down in Shannon County, Missouri at 12:45 p.m. Central Time and spent three hours and 45 minutes on the ground carving a 219-mile-long path across southern Illinois and into southwestern Indiana! 695 people died, and over 2,000 were injured.
Today’s meteorologists estimate that the tornado had winds of over 300 miles per hour which would place it into the EF-5 category.2
1“Understand Tornado Alerts.” National Weather Service, National Oceanic and Atmospheric Administration, https://www.weather.gov/safety/tornado-ww
2“1925 Tri-State Tornado.” Wikipedia Wikimedia Foundation, Inc., https://en.wikipedia.org/wiki/1925_tri-state_tornado