Climate researchers say a strong La Niña will bring below-average rainfall to Southern California this winter.
La Niña is defined as cooler than normal sea-surface temperatures in the central and eastern tropical Pacific Ocean that change global weather patterns. Those patterns affect areas that include California and the Western United States.
Researchers said a strong La Niña means below-normal rainfall for Southern California, and a wet fall and dry spring for Northern California.
La Niña conditions happen every few years and can last as long as two years. This year that's what University of Colorado researcher Klaus Wolter is forecasting.
"I believe that the odds are much enhanced that we have a La Niña that goes on and on rather than disappear again," said Wolter.
Wolter had an unusual description for what a stronger La Niña is like.
"[It's] sort of like the ending of, what was that movie in the 1980s with Glenn Close? Fatal Attraction? Fatal Attraction, you know where she keeps coming back," said Wolter, laughing.
Wolter said the current La Niña may influence our weather in the same way.
"The late 90s events were like that too, where we had a three-year La Niña from 1998-2001," said Wolter. "And if you look at detail at what happened in those years, they always came back in the fall and they always looked in the spring like they were going away. This one is actually bigger than 1998 in my book."
Bigger is not a good thing for California's thirsty farms and cities.
Even if there's less rain and snow this winter in California, however, Jeanine Jones with the state's Department of Water Resources, said the water supply is looking good for 2011.
"We're going into the new water year with generally pretty good reservoir storage statewide," said Jones. "So thanks to last year's precipitation we were able to catch up on storage."
Jones said only a couple of reservoirs are significantly below normal.
But it's not water supply that worries researcher Wolter this winter.
"If we go through this winter on the dry side, I would say watch out in the Spring for maybe some early season fires in Southern California," said Wolter. "But in terms of the water supply, given the reservoir situation and given my forecast for Northern California, I'm not that concerned this year, I am more concerned about the year after this."
Wolter has monitored the weather cycles in the western U.S. for more than 10 years. He said the fall rains will make a difference.
"Certainly in the upper Colorado, certainly in parts of California, having a wet fall really helps lubricate, if you will, the stream beds to be more efficient and give more runoff in the spring," said Wolter. "That's a really good sign from the get-go."
The strong La Niña also means less extreme weather, such as rainstorms of one-inch or greater in San Diego this winter.
Scripps Institution of Oceanography researcher Dan Cayan said we may get some heavy rains now, but big storms are less likely December through March.
"The chances of getting heavy events are really diminished under a La Niña that's borne out by looking at the record going back to 1950," said Cayan.
Cayan said less heavy rainfall also means reduced risk of floods.
But Cayan, like Wolter, worries the dry times could create extreme fire danger next spring.
