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Inland Northwest twisters unusual; rarely devastating

As we get further along into spring, the chances for thunderstorms and even severe weather increase. In the past, there have been instances of tornadic activity in our region. However, the majority of the extreme weather occurs in the Great Plains and Midwest.

During spring, that part of the country is referred to as Tornado Alley. Because of the Rocky Mountains, we will never see the severity of tornadic activity, an F5, which occurs in the Great Plains and Midwest.

However, in our regionthere have been numerous occasions of damaging winds and hail. In 2006, there were 48 warnings issued between July 1 to 15 for thunderstorm activity. The number of warnings during that period were more than the totals of 2005, 2004 and 2003. Last year, thunderstorm activity was less than normal, but is expected to increase this year.

One of the worst severe weather and tornado outbreaks in our region occurred on May 31, 1997. A record six tornadoes touched down in Washington on that day. The previous mark for an entire year for tornadoes was four in 1989. Before 1997 was over, a record 14 twisters were reported in Washington.

The intensity of a tornado is measured by the Fujita scale. It examines the damage caused by the twister. An F0 and F1 tornado inflicts generally minor damage, but an F5, the most severe, causes widespread destruction.

On May 31, 1997, four F1 twisters hit Stevens and Spokane counties with one F1 tornado striking Athol in North Idaho with an F0 spotted near Lewiston. Severe thunderstorms also produced hail 2 to 3 inches in diameter, heavy rainfall and wind gusts more than 80 mph. Fortunately, there were no deaths or injuries.

The deadliest tornado outbreak in Washington’s history happened on April 5, 1972. An F3 twister struck Vancouver and swept through a grocery store, bowling alley and grade school. Another F3 tornado touched down west of Spokane with an F2 twister seen in rural Stevens County. There were a total of six deaths, 300 injuries and $50 million in damages.

In 2010, we’ve already seen two days with a thunderstorm at the airport. During a normal year, we receive approximately a dozen thunderstorms.

As far as our weather is concerned, the spring of 2010 still appears as if it will be generally cooler and wetter than normal with the weakening of El Niño, the warmer-than-normal, sea-surface temperature event.

But, there will be much warmer days ahead in late June, July and August and at least the first 10 days of September. In fact, we may see as many as 25 days near or above 90 degrees this blistering summer of 2010.