La Nina Powers Wild Weather Phenomenon

By Ben Tracy

September 2, 2011 7:25 PM (CBS News)

LOS ANGELES - So far, this has been a rough year for wild weather from severe drought in the Southwest, record snow in the Rockies, to unusually cool temperatures in the Pacific Northwest.

Climate experts tell CBS News correspondent Ben Tracy a strange phenomenon is behind a lot of it, from sea to shining sea.

The Pacific Ocean, with its 20 foot waves, is giving California's coast a beating, and some of the best surf in years. It's powered by an Antarctic storm - but something else is brewing in those waters.

"It's deja-vu all over again," says NASA climatologist Bill Patzert. "Looking back over the last eight months we've definitely had weather whiplash and weather mayhem and much of this was due to the presence of La Nina."

La Nina occurrs when water temperatures in the Pacific Ocean near the equator dramatically cool. That's what happened this past winter. The La Nina pushed the jet stream over the U.S. to the north and made regular weather patterns more extreme.

That's why the Sierra Nevada mountains saw more than 50 feet of snow, spring rains flooded the Midwest, while Texas was kept bone dry - its worst drought in half a century.

"The waves that recently pounded the West Coast are not caused by La Nina - but increasingly scientists believe another La Nina is developing out in the Pacific and that could cause more unpredictable weather."

This week the United Nations doubled its probablity of another La Nina from 25 percent to 50 percent. It's not clear if climate change is having an impact on La Nina events - they generally occur every three to five years - not back to back.

"Temperatures at the equator are starting to drop and that really is the footprint of La Nina," Patzert says.

"All the smart money is on a double bounce for La Nina."

That could mean more hurricanes hitting the U.S. The jet stream's winds normally break up hurricanes. But when La Nina kicks the jet stream north, hurricanes can barrel into the Gulf of Mexico, or like Irene - slide right up the East Coast.

If there's any good news, experts say this La Nina should be weaker than the last - a shorter but still unwelcome encore

Source: CBS News