OREGON STATE UNIVERSITY

Utah tornado part of larger weather systems

08/11/1999

CORVALLIS - The substantial tornado that hit Salt Lake City Wednesday afternoon was not only very rare for that location, but also apparently evolved out of seasonal weather patterns that are causing violent storms throughout the Great Basin and Southwest, including some even in Oregon.

According to George Taylor, the state climatologist at Oregon State University, the "monsoon season" for the southwestern U.S. is now at its peak as warm, humid air comes rolling north from the Gulf of Mexico. And a current trough of low pressure off the Pacific Northwest coast is helping to amplify the south to north air flows.

One of the most recent tornado victims today was Salt Lake City, where early news reports suggest 100 or more people were injured and many buildings were damaged, including the roof of the Delta Center, home of the Utah Jazz in the National Basketball Association.

"Tornadoes in Utah tend to be similar to those in most of Oregon, very rare and very weak," Taylor said. "In one recent 25 year period Utah had only 32 tornadoes, compared to 1,336 in Oklahoma. And the fact this storm went right through downtown Salt Lake City is even more unusual."

But storms able to do the significant damage today's tornado did in Utah are not unheard of, Taylor said, and similar events may even happen in Oregon.

"Last night we had one-and-three quarter inch hail in northern Klamath County, and 1.6 inches of rain in Central Point," Taylor said. "Bend was hit with three-quarter inch hail and local flooding that closed three of the four underpasses on U.S. Highway 97. With the current weather patterns, it wouldn't be all that surprising to see more severe thunderstorms and perhaps even tornadoes in Oregon this week."

According to Taylor, states of the intermountain West such as Oregon and Utah are often spared large, damaging tornadoes because they are too dry.

In "tornado alley"- a stretch of the central plains running from Texas northeast to Oklahoma, Kansas, Nebraska, Iowa and Missouri that is far and away the most tornado-prone region on the face of the Earth - incredibly intense storms are triggered by a combination of high humidity and large temperature differences from north to south.

The air of places such as Oregon or Utah usually holds far less water vapor than the atmosphere of tornado alley. And that water vapor is critical to the formation of large tornadoes.