National Weather Service Weather Forecast Office

Tornado Safety

Technically defined, a tornado is a violent rotating column in contact with the ground that is attached to a parent thunderstorm.  On a local scale it is the most destructive of all meteorological phenomena.  Many tornadoes last for only a few minutes and are on the ground for a few miles.  Other tornadoes can persist for hours, travel more than a hundred miles, and have a mile wide path. 

In Wyoming, tornadoes are relatively rare compared with the Midwest and Plains states.  In central Oklahoma, (the national maximum) tornadoes occur about 20 times more frequently than in the same size area in central Wyoming. Yet certain parts of Wyoming are significantly more prone to these destructive storms than are other parts.  In general, the eastern half of the state is more likely to experience tornadoes due mainly to the increase of available moisture at the lower levels of the atmosphere.

Across western and central Wyoming, 76% of all reported tornadoes occur between 2:00 p.m. and 7:00 p.m. local time.  Additionally,  approximately 50% of all reported tornadoes are rated F-0 (zero), based on the Fujita Tornado Scale.  On this scale an index of zero signifies light damage, a value of 5 indicates incredible damage (F-5 damage path through Oklahoma) and intermediate levels represent intermediate levels of destruction.  During the years 1950 to 2004, 132 tornadoes were reported in the NWS Riverton County Warning Area.  These tornadoes killed one person and injured 15.  The most destructive tornado in Wyoming's history ripped through northern Cheyenne on July 16, 1979, leaving 2 dead, 57 injured, and hundreds of homes destroyed.  It rated only a value of 3 on the Fujita scale.  The strongest tornado (as ranked on the Fujita Scale) to occur in Wyoming struck Teton County and portions of Yellowstone National Park on July 21, 1987.  The tornado downed over 1 million trees across 15,000 acres and occurred at over 10,000 feet in elevation.

If a tornado warning is issued for your area you should move immediately to a substantial building or shelter.  move to the lowest floor of your home.  Go to an interior room (such as a closet or bathroom) and cover your head and body.  Share these important safety rules with your family and friends.  Following these simple safety rules could save your life.  Tornadoes are not all that rare, with approximately 12 reported each year across the Cowboy State.  The NWS Riverton County Warning Area experiences more than two tornadoes each year.

Tornado near Lander September 30, 2004 Photo Courtesy of Ernie Over