Tornado season off to a slow start

The last several months saw more extreme weather across the U.S., especially in the central portions of the country. Many areas went from record cold to record warmth. Despite the big change in temperature, the month of May had the lowest number of tornadoes in the central portions of the country in years.

According to Rutgers Global Snow Lab, for 22 states east of the Rockies, April was in the top 10 for the coldest in history. As has been the case with this wild cycle of “extremes,” temperatures went from cold in April to above average in May. Many areas, especially east of the Rockies, reported average temperatures soaring as much as 20 to 30 degrees higher from April to May. That’s a pretty big swing.

Along with extremes in temperature, there were record amounts of precipitation along the East Coast. Many major cities from Florida northward to Atlantic City, N.J., reported their wettest May in recorded history. Nearly 15 inches of rain fell in Asheville, N.C., last month as widespread flooding was seen.

This is the time of year when we often hear about an increase in tornado activity in the U.S. So far, the Storm Prediction Center reports only 431 tornadoes across the U.S. for the 2018 season. The normal amount is 779 twisters through May, which based on a 10-year average.

May is usually the month when we often hear about the big tornadoes. Last month, there were about 113 confirmed sightings around the country. However, there were four twisters that touched down in New York’s Hudson Valley in the middle of last month, making it the worst outbreak there in May in 16 years. The average number of tornadoes for May is 276 with the majority occurring in Texas (43), Oklahoma (28) and Kansas (38). Both Idaho and Washington average one tornado during the month of May.

In an average year, there are about 1,200 tornadoes sighted in the U.S., more than any other place in the world. In 2017, there were an above normal 1,418 twisters that resulted in about $5 billion in damage. More than 60 percent of all U.S. tornadoes each year occur in what is called, “Tornado Alley,” which stretches from Texas and Oklahoma northward through Kansas and eastern Colorado into Nebraska and Iowa.

Fortunately, in the calmer Inland Empire, the Cascade Mountains to the west and the Rockies to the east usually protect us from the extremely powerful thunderstorm activity. But, every spring season, and sometimes during the hot summer months, we do see an occasional period of extreme weather conditions.

Tornado intensities are measured using the Enhanced Fujita Scale, with an EF5 being the most destructive. This scale was implemented in early 2007 and has the same design as the original Fujita scale, which included ranges from an F0 to an F5. Last month, there were no reports of tornadoes in the EF4 or EF5 range in the U.S.

Idaho averages three tornadoes per year. One of the worst severe weather and tornado outbreaks ever seen in our region occurred on May 31, 1997, across eastern Washington and northern Idaho. On that day, four F1 twisters hit Stevens and Spokane counties, with one F1 tornado striking Athol in northern Idaho and an F0 spotted near Lewiston. Severe thunderstorms also produced hail up to 2-3 inches in diameter, very heavy rainfall and wind gusts of over 80 mph. Fortunately, there were no deaths or injuries.

An estimated record 10 tornadoes touched down in Washington and Idaho on May 31, 1997. In Kootenai County, an F2 was reported, one of the largest ever seen in Idaho. An F1 was reported in Jefferson County.

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In terms of our local weather, we’ll have mostly dry conditions this week with temperatures cooling down today. But, toward the end of the week, we’ll have some nice afternoons with highs in the 70s to near 80 degrees. Winds will also be breezy at times this week.

Some showers and a few thunderstorms are possible this weekend and again toward the middle of the month. However, it appears we’re getting into that drier than normal weather pattern for the late spring and summer season. Cliff and I still believe that the summer of 2018 will be drier than normal, but not as dry as last year when we had those long stretches without moisture.

If sea-surface temperatures remain the same and our weather patterns keep evolving like we think they are going to, then rainfall should start to pick up again by late summer or fall to above normal levels once again. Once again, time will tell.

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Contact Randy Mann at randy@longrangeweather.com.