Even without a tornado, a severe thunderstorm can be a damaging and life-threatening event. Deaths and injuries occasionally occur from strong thunderstorm winds. Large hail can be produced by these storms.
The National Weather Service defines a thunderstorm as "SEVERE" when wind speeds reach 58 mph or stronger and hail is produced that is 3/4 inch in diameter or larger. When storms reach this magnitude, tornadoes can be produced.
Downward rushing currents of air, or downdrafts, occur along the leading edge of almost all thunderstorms and along the trailing edge as well. These storms can produce winds as damaging as those of a tornado. Strong localized downdrafts are called "DOWNBURSTS". When downbursts ocur they are often mistaken for a tornado.
The potential for deaths, injuries and damage from severe thunderstorms make it imperative that we heed severe thunderstorm warnings. Just like Tornado Watches or Tornado Warnings, watches and warnings are issued for areas threatened by severe thunderstorms.
When a severe thunderstorm warning is issued, move to a safe place immediately and stay away from windows.
See Lightning Safety for a more thorough discussion of what to do when lightning is present.