Tornadoes rare in our region
Thunderstorm activity in our region has been relatively quiet, thanks to La Niña, the cooler than normal sea-surface temperature event in the waters of the south-central Pacific. However, severe weather conditions can occur often in the Inland Empire in June, July and August.
A typical strong thunderstorm in our region will usually produce very strong winds, hail, lightning and torrential downpours, and sometimes tornadoes. Tornadoes, especially strong ones, are rare in the Northwest. Idaho averages three twisters a year while Washington and Oregon normally see two per year. By contrast, there are an average of 139 twisters per year in Texas, 57 in Oklahoma and 55 in Kansas and Florida.
The strong tornadoes occur east of the Rockies. The high mountain range protects much of the West from the moist and warm air from the Gulf of Mexico that’s a necessary ingredient to produce the very strong (F5) twisters. Twisters are measured on the Fujita scale that ranges from a small tornado, F1, to F5, the strongest and most destructive.
Earlier this season, 22 people were killed as the result of tornadoes which swept across Oklahoma, Missouri and Georgia. During the first week of February, the death toll was even higher with 57 fatalities attributed to 82 confirmed tornadoes across the lower Ohio Valley and Southern U.S. The only tornado reported west of the Rockies occurred when a rare winter tornado swept through Vancouver, Wash., on January 10.
The worst outbreak of tornadoes in U.S. history occurred on April 3-4, 1974, the so-called “Super Outbreak.” A total of 148 twisters touched down in 13 states from Illinois and Indiana south into Mississippi and Alabama. Over a period of 16 to 18 hours a 330 people were killed and 5,484 were injured. The property damage estimate was $600 million.
There are approximately 1,200 tornadoes sighted in the U.S. in an average year, more than any other place in the world. More than 60 percent of all U.S. tornadoes occur in what is called Tornado Alley, which stretches from Texas and Oklahoma northward through Kansas and eastern Colorado into Nebraska and Iowa.
Wind-measuring instruments like anemometers are often destroyed by tornadic blasts exceeding 250 mph. Tornadoes are nature’s most destructive storms. 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.
The deadliest outbreak of tornadoes in our part of the country occurred on April 5-6 in 1972. There were six fatalities and more than 300 injuries in Eastern Washington. Damage totals exceeded $50 million. The largest twisters observed received an F3 rating.
On May 31, 1997, four F1 tornadoes hit Stevens and Spokane counties. Another F1 tornado was sighted near Athol, Idaho. Baseball-size hail damaged property in the Lewiston area. There were no deaths or injuries.
The overall weather pattern into mid-June should be wet, likely with several strong thunderstorms accompanied by lightning, heavy downpours, damaging winds and pea-size hail.
From the end of June through at least mid-September, there should be generally warmer-than-normal temperatures with a bit less precipitation than usual for this 75-day period.