Tornadoes aren’t just for Kansas

With forecasters saying tornadoes are a possibility Thursday, some are wondering how unusual such weather conditions are.

Less rare than one might think, according to Bill Patzert, a climatologist for the Jet Propulsion Laboratory in La Cañada Flintridge.

Since 1950, there have been an average of about five a year in California. Some years there are none, but in 1992 there were 20, Patzert said.

By the standards of the massive tornadoes that destroy small towns in places like Oklahoma and Texas, California’s tornadoes are small, but they can still be destructive within a smaller scale.

In 1983, a twister plowed a path one-third of a mile wide alongside the Harbor Freeway at rush hour, from 51st Street to the southern edge of downtown.

The tornado tore roofs from houses, overturned cars and snapped large trees and utility poles.

Tornadoes can occur when very cold, unstable air flows over warm, dry land, he said. “The severe thunderstorms which produce tornadoes form where cold dry polar air meets warm moist tropical air,” Patzert said. “Like we’re seeing now.”

hector.becerra@latimes.com