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The Spokesman-Review Newspaper
Spokane, Washington  Est. May 19, 1883

Supercells lead to deadly thunderstorms

Michelle Boss

Last Monday, severe thunderstorms plowed through the state of Oklahoma, spawning dozens of tornadoes. Damage was extensive and there were several fatalities. These tornadoes were produced by a special type of thunderstorm, called a supercell.

A supercell thunderstorm is one that exhibits strong rotation, and it’s these types of thunderstorms that have the best chance of producing tornadoes. Tornadoes can be produced by non-supercell storms (like the type we usually see across the Inland Northwest), but these tornadoes are usually not as strong nor long-lived.

After the storms, there was much discussion about the EF-rating of the tornadoes. The “EF-scale” stands for the “enhanced Fujita scale” named after well-known tornado researcher Ted Fujita (1920-1998) of the University of Chicago. He developed a scale that gave a tornado an intensity rating based on the damage that it did. It is not the best way to categorize tornadoes based on strength/windspeed, however, because the rating has nothing to do with any actual measured wind speeds of the tornado, only the damage that was caused.

In other words, a large tornado that destroys a house down to its foundation might get an EF-4 rating (on a scale of 1-5), while a similar tornado that passes through a field of grass and small trees would be rated much lower. The Fujita scale (F-scale) which Fujita established in the 1970s, was revamped a few years ago based on new research concerning wind speeds and damage, and in 2006 was renamed the “EF-scale.”

Supercell thunderstorms and their accompanying tornadoes are very rare across the Inland Northwest. Both Idaho and Washington only average 1-2 tornadoes each year, and they are usually less intense than the supercell tornadoes of the Great Plains. What we see much more often are whirlwinds or dust devils, which have the potential to produce minor damage, but are formed by a completely different process than tornadoes. While tornadoes are produced by thunderstorms and descend to the ground, dust devils and other types of minor whirlwinds are formed at the surface.

Michelle can be reached at weatherboss@comcast. net.