As El Niño grows stronger, so does hope for wet winter

This satellite image depicts formation of a mild El Niño current in the Pacific Ocean in 2006, shown as the large swath of red through the center of the scene. Weather scientists say a stronger El Niño appears to be forming this autumn, which could portend average or above average precipitation in California. [Image from NASA]

Conditions are developing that could provide wet weather patterns to California this winter, according to weather experts. Weather scientists projected a better water year at a Winter Outlook Workshop sponsored by the California Department of Water Resources in San Diego last week.

In addition, three long-range weather forecasts also project average to above average precipitation for most of California this coming winter. The National Weather Service Climate Prediction Center, AccuWeather—which provides weather forecasts for Ag Alert®—and The Old Farmer's Almanac all say it will be a wet winter.

Meteorologists acknowledge forecasts more than three days out are iffy, as conditions can change. However, they say longer range forecasts now look more positive for at least normal precipitation in California, though they can't predict what proportion of it will fall as rain or as snow.

The National Weather Service Climate Prediction Center now forecasts average precipitation for all of California in November through January, after upgrading its precipitation forecasts. Until mid-October, it had projected another dry year.

The development of the El Niño current off the coast of South America is what has changed the long-term outlook. University of Colorado climate researcher Klaus Wolter told the DWR conference the El Niño event intensified during the last three weeks of October.

El Niño is what fishermen called the warm water current when they noticed it off the coast of Peru around Christmastime. The El Niño current does not create storms, but causes a shift in weather patterns that makes some areas more susceptible to storm formations. The phenomenon does not always bring heavy precipitation to California, but this year it appears to be intensifying, which usually does mean more precipitation for the state.

During the 18 El Niño events since 1950, rainfall in Central California has been above average half the time and below average half the time. Below average precipitation usually happens when the El Niño current is weak or mild. Most computer models project this one to strengthen in the late fall and winter months, even as the warm current is intensifying right now.

Wolter said the effects of a strong El Niño often persist into the spring, bringing unseasonably late storms.

"If you want water this winter, you really have to root for a strong El Niño," Wolter said. "If El Niño is reasonably strong this winter, don't be surprised if you get a wet spring."

He also expressed faith in a European computer model that signals a strengthening El Niño throughout 2010.

AccuWeather meteorologist Ken Clark said some computer models suggest a weakening El Niño in January or February.

"If that happens," he added, "it could offset California rainfall." But for now, he said, it looks like a wet winter for most of the state.

Clark said the strength of Hurricane Rick and the development of Hurricane Neki south of Hawaii tells him the warm current is getting stronger. He said there is a better-than-average chance Central and Southern California will have average or above average precipitation this season.

But Northern California is a different matter, he said. The Pacific Northwest should be drier than average, after having had above average precipitation the last four years. Northern California may get some moisture from storms that pass over Central California, Clark said, but he doubts there will be above average precipitation in the northern quarter of the state this year.

"Wet typhoon moisture that kept intensifying as the storm crossed the Pacific Ocean from Japan is what caused the large amounts of rain in California during the Oct. 13 storm," Clark said.

State Department of Water Resources hydrologist Maury Roos said that, historically, rain in October does not foretell either a wet or dry winter. But the mid-October storm dropped 9 percent of annual precipitation in the Northern Sierra, which is about 5 percent above average for this time of year. Roos said he remains optimistic this will develop into a good year for precipitation.

The Old Farmer's Almanac predicts wet weather from November through January. Its forecasters use a variety of criteria in their projections, including sunspots, and say the sun is in a period of few sunstorms right now.

DWR Senior Meteorologist Elissa Lynn said she agrees with the forecasts for good precipitation for Central and Southern California. But she predicts a near-average snowpack for the Northern Sierra.

Some speakers at the DWR workshop expressed less optimistic outlooks for the winter, including U.S. Geological Survey research hydrologist Mike Dettinger.

"I'm cautiously optimistic that we may get a normal year," Dettinger said, but added, "I'm really dubious about whether we'll get a really good year."

However, he noted, even a normal year would be better than the past three dry ones.

(Ron Miller is a reporter for Ag Alert. He may be contacted at rmiller@cfbf.com.)

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