La Nina likely to return this winter
For the second straight year, a La Nina is developing in the equatorial Pacific, raising the possibility that San Diego County and the rest of Southern California could experience a drier-than-normal winter. But forecasters are being cautious; last winter was wetter than usual in most areas.
"La Nina usually indicates that things will be drier, but it didn't work out that way last time," said Phil Gonsalves, a forecaster at the National Weather Service.
San Diego experienced one of the rainiest Decembers on record, resulting in flooding that nearly delayed the Pointsettia Bowl at Qualcomm Stadium.
The U.S. Climate Prediction Center says in an online advisory that the La Nina now taking shape will "gradually strengthen and continue into the northern hemisphere winter 2011-2012." (Full advisory).
The Scripps Institution of Oceanography in La Jolla says it is "forecasting cool La Niña conditions this winter (December 2011 through February 2012)."
La Nina is a periodic climate change that occurs when sea surface temperatures in the central and eastern tropical Pacific become cooler than normal. And trade winds blow more to the west. That combination tends to shift storms to the western Pacific, limiting rainfall in Southern California.
But the last rainy season was a wet one in San Diego County. From 1981 to 2000, Lindbergh Field averaged 10.34'' of rain during a season that extends from July 1 to June 30th. Last season, the airport recorded 12.62'' of precipitation, and many inland areas recorded rainfall that was at least 5'' above normal.
Such figures represent an anomaly. There have been 23 La Nina events between 1949 and early 2011. San Diego recorded above average rain during only two of those events. (Read Rob Krier's January 2010 overview.)