Tornado Watch:  Severe thunderstorms and tornadoes are possible within and near the watch area for the duration of the watch.  Coverage area:  Areas of states to multiple states.  Length of time: 4-8 hours.
 
P.D.S. Tornado Watch:  Severe thunderstorms and long-lived, long track destructive tornadoes are possible within and near the watch area for the duration of the watch.  P.D.S. stands for "Particularly Dangerous Situation."  Viewers are encouraged to stay abreast of that latest updates and possible warnings.  Coverage area:  Areas of states to multiple states.  Length of time: 4-8 hours.
 
Tornado Warning:  A tornado has been indicated by radar or has been confirmed by a trained weather spotters.  Seek shelter immediately!  Do not wait to hear tornado sirens to sound.  Coverage area:  Small areas of counties to entire counties.  Length of time: 20-60 minutes.
 
Tornado Emergency:  A large and destructive tornado has been confirmed on the ground and moving towards a large populated area.  Those in a Tornado Emergency area should seek shelter BELOW GROUND IMMEDIATELY.  Shelter above ground may not be sufficient to survive the storm.  Do not wait to hear tornado sirens to sound.  Coverage area:  Small areas of counties to entire counties.  Length of time: 20-60 minutes.