Weather watchers fear that a cooling cycle in the Pacific Ocean will bring what California needs least: another drought year.
The National Weather Service announced this week that a La Niña pattern has taken hold across the Pacific. Marked by a cooling trend in the waters of the equatorial ocean, La Niña usually diverts the jet stream into Canada, bringing dry conditions to California.
La Niña was present last winter, and it brought the second dry year in a row. Rain and snowfall nearly disappeared in Northern California after January last year.
This year's La Niña looks stronger and longer-lasting, said Bill Patzert, a climatologist at NASA's Jet Propulsion Laboratory in Pasadena.
"The dice are pretty loaded here against a big snowpack and a heavy rainfall," he said. "But you know, this is one of those things where I really love to be wrong."
As of 4 p.m. Friday, Modesto had received 2.99 inches of rain since July 1, the start of the rain year, the Modesto Irrigation District reported. That's about two-thirds of an inch less than the same time last year and nearly 1½ inches below normal for this time of year.
But December brought a week of welcome snowstorms to the Sierra Nevada, California's water bank. Snow totals for the winter exceed last year at this time but still are below normal.
A "Pineapple Express" storm predicted to hit Central California on Christmas Eve, bringing heavy snow and torrential rain, did not materialize. It turns out La Niña was at least partly to blame.
Though it did rain and snow over Christmas, Dave Reynolds, meteorologist in charge of the weather service's Bay Area bureau, said currents associated with La Niña pushed the heavy precipitation north of California. More of the same could be ahead.
"Needless to say, this pattern is not good for the water supply," Reynolds said via e-mail.
El Niño is the more familiar pattern. Named after the Spanish term for "Christ child," because it usually emerges in the Pacific around Christmas, El Niño warms the equatorial Pacific and typically brings consistent wet weather to California.
La Niña, or "girl child," is harder to predict. It has brought terrible droughts and terrible flooding to California.
The floods have come in La Niña years because it creates better conditions for those Pineapple Express storms, if they can break through the altered jet stream.
Absent such storms, odds favor dry weather.
"We're remaining hopeful the pattern will change enough that we begin to get some repeated storms into California that will help out our water supply," said Rob Hartman, hydrologist in charge at the weather service office in Sacramento.