Powerful tornadoes sweeping across the Great Plains and Midwest have been in the headlines. During the spring and summer, conditions become very favorable for the development of severe thunderstorms and tornadoes, especially east of the Rocky Mountains.
Tornadoes, especially strong ones, are rare in the northwestern United States, as the high mountain range of the Rockies protects much of the West from the warm Gulf of Mexico air that’s a necessary ingredient to produce strong twisters. During a typical year, Idaho averages three tornadoes while Washington and Oregon normally see two. Texas sees an average of 139 twisters. Oklahoma experiences 57 tornadoes and Kansas and Florida 55. Tornadoes are classified from weak F0 to the very strong F5 rating.
There are about 1,200 tornadoes in the U.S. each year, more than any other place in the world. In fact, every state, including Alaska and Hawaii, have reported a tornado. More than 60 percent of all U.S. twisters occur in Tornado Alley, which stretches from Texas and Oklahoma northward through Kansas and eastern Colorado into Nebraska and Iowa. Twisters can be spawned as warm, moist air from the Gulf of Mexico collides with cooler air from Canada in spring and summer. But, in the central U.S., twisters can be spotted at any time of year.
Tornadoes are nature’s most destructive storms – wind-measuring instruments like anemometers are often destroyed by tornadic blasts exceeding 250 mph. Pieces of straw, for example, can penetrate wood at wind speeds exceeding 230 mph. The strongest wind speed ever measured in a tornado was 280 mph in Kansas in 1997. However, wind gusts are estimated at much faster than300 mph.
The deadliest outbreak of tornadoes in our part of the country occurred on April 5 and 6, 1972. The largest twisters observed in Spokane County was an F2, on June 15, 1954, and another on May 6, 1957. On May 31, 1997, four F1 tornadoes hit Stevens and Spokane counties in Eastern Washington, and near Athol in Idaho.