Winter Forecast 2011-12: Could Southern California Get Crushed Again?

December 2010 became one of the wettest Decembers on record for Los Angeles with nearly a year’s worth of rain falling in just one month.

While a few heavy rain events cannot be completely ruled out in Los Angeles and San Diego this year, the focus of stormy weather this winter is predicted to be farther north, according to the AccuWeather.com Long-Range Forecasting Team.

Overall, this winter is expected to be fairly typical in Southern California with near-normal rainfall and temperatures. However, it may be a long stretch toward the end for people who become anxious for spring, as unusually chilly conditions will take hold in February.

The Pineapple Express: A Key Winter Player for California

It was the famed “Pineapple Express,” a phenomenon that occurs when a strong, persistent flow of tropical moisture sets up from the Hawaiian Islands to the West Coast of the U.S.; this flow brought the historic storms to Southern California in December 2010. More than 10 inches of rain fell last December in Los Angeles, a city that typically receives a little less than 15 inches of rain in an entire year.

The Pineapple Express could develop for a time again this winter, though it would most likely be aimed at northern and central California.

“Last year, California was hit hard when the Pineapple Express set up from Dec. 17-22, producing massive flooding and 13 feet of snow in the Sierra,” explained Paul Pastelok, AccuWeather.com Expert Long-Range Meteorologist and leader of the Long-Range Forecasting Team. “The Pineapple Express could develop for a period this winter and take aim at northern and central California. That could lead to monster snowfall and heavy valley rain with the risk of flooding and mudslides.”

Must Be Careful with La Ninas

La Nina, a phenomenon that occurs when sea surface temperatures across the equatorial central and eastern Pacific are below normal, has a strong influence on the jet stream and weather patterns, including the Pineapple Express, that set up across the United States.

The general trend for La Nina winters is for Southern California to be drier than normal with above-average temperatures. However, as evidenced by last year’s record-shattering December storms, there can be exceptions.

“While a La Nina like the one we are expecting this winter typically brings lower-than-normal precipitation to Southern California and the Southwest, the concern this year is that something similar to what happened last year could happen again,” stated AccuWeather.com Senior Meteorologist and Western Expert Ken Clark. “Storms may be far enough south or wet enough that rainfall could be higher than what is typically expected during a La Nina.”

Southern California had an incredibly rough start to winter last year when a series of monster storm systems brought epic rain and flooding. December 2010 became one of the wettest Decembers on record for Los Angeles with nearly a year’s worth of rain falling in just one month.

Month-to-Month Breakdown

In general, the Long-Range Forecasting Team expects December to be fairly typical for Southern California with near-normal precipitation and near- to slightly above-normal temperatures. January is forecast to turn out drier than usual, though temperatures will overall remain near normal.

From late January into February, however, a transition to chillier weather is predicted to take place, as the overall jet stream pattern over the West Coast undergoes some major changes. Precipitation in February is likely to be near to slightly below normal.

Winter is California’s wettest season. For Los Angeles and San Diego, February is usually the wettest month of the year with January being a close second.