Wild and deadly weather: Is La Nina to blame?

A tornado moves through Tuscaloosa, Ala. April 27, 2011. A wave of severe storms laced with tornadoes strafed the South on Wednesday, killing nearly 200 people across the South. A
Tuscaloosa tornado

It's been a spring of records -- heat, floods, tornadoes. There appears to be something behind it, reports CBS News correspondent John Blackstone. Remember the weather effect known as "El Nino"? Well, meet La Nina.

In Hawaii, in June, there's snow, with people on sleds instead of surfboards. The islands' tallest volcanic peak does see snow in winter, but it's been 30 years since there's been anything like this.

"I don't know if it has to do with the world climate change or what but it's sort of cool," said Pam Akao, of Wimea on the Big Island.

Meanwhile, much of the eastern U.S. is experiencing a record heat wave. Almost every part of the country has experienced some extreme weather lately.

Some blame La Nina, the cyclical cooling of the Pacific near the equator. In La Nina years, rain patterns across the country change. But this La Nina has now been declared over and may be only a small part of a complicated mix.

"A lot of this comes down the chaos in the atmosphere," said meteorologist Jan Null of San Francisco State University. "There are so many things going on and we just don't have the tools to measure every single one of them."

One of the big things going on is a particularly strong jet stream. For much of this year, high level winds have been stuck in a pattern that brought lots of rain and snow to the west and north and kept the plains and south east exceptionally dry.

The result: terrible floods in the Mississippi basin and drought in the southwest, part of the reason Arizona is now burning.

Photos: Disasters of 2011

But perhaps the biggest weather troublemaker has been in the Gulf of Mexico where sea surface temperatures have been almost 2 degrees above average.

Warm moist air from the Gulf meeting the powerful jet stream provided the energy that created historically destructive tornadoes that killed 525 people -- the most since 1950.

While weather records of some kind are set almost every year, this year has seen tornadoes, floods, drought and wildfire of historic proportions -- and having all those records in one year, in fact in little more than a month, is unprecedented.

  • John Blackstone

    From his base in San Francisco, CBS News correspondent John Blackstone covers breaking stories throughout the West. That often means he is on the scene of wildfires, earthquakes, floods, hurricanes and rumbling volcanoes. He also reports on the high-tech industry in Silicon Valley and on social and economic trends that frequently begin in the West.