Environment & Science

El Niño: What to expect in SoCal this winter

A man crosses a street during a steady rainfall on September 15, 2015 in Los Angeles, California, as a low-pressure system filled with moisture from a former tropical cyclone unleashed heavy rain. At least eight people were pulled into rain-swollen San Gabriel River Tuesday as a storm drenched Southern California, flooding freeways and knocking out power.  AFP PHOTO /FREDERIC J.BROWN        (Photo credit should read FREDERIC J. BROWN/AFP/Getty Images)
A man crosses a street during a steady rainfall on September 15, 2015 in Los Angeles, California, as a low-pressure system filled with moisture from a former tropical cyclone unleashed heavy rain. At least eight people were pulled into rain-swollen San Gabriel River Tuesday as a storm drenched Southern California, flooding freeways and knocking out power. AFP PHOTO /FREDERIC J.BROWN (Photo credit should read FREDERIC J. BROWN/AFP/Getty Images)
File photo by Frederic J. Brown/AFP/Getty Images

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Winter is coming and with it the ever growing chance for serious rains in Southern California, thanks to El Niño.

The latest report from the National Oceanic and Atmospheric Administration found that ocean temperatures in some key areas of the Pacific associated with El Nino are more that 5 degrees Fahrenheit warmer than average. The more these waters heat up, the stronger the El Niño gets.

So should we expect three months of gray, rainy skies in Southern California this winter? 

Dan Cayan, a climate researcher with the Scripps Institution of Oceanography.

"Even in the best of winters, most of our days are not stormy," Cayan said.

 El Niño typically bends the jet stream that carries rain to the Pacific Northwest and points it at Southern California.

He likened the effect to a train of storms that hits the region one after another but with calm periods in between.

"You could get two to three days of storminess and then usually get an interlude," Cayan said. "It’s very unusual for us to get a week in a row of constant rain."

Based on data from previous El Niño events, Cayan thinks we can expect about one-and-half to two times as many storms this winter as we'd see in an average year. He described it as a handful of major storms, but not dozens of them.

The rain should start in earnest around late December or early January.

Given the historic drought in California, the water will be welcome, especially if it falls as snow in the Sierra Nevada mountains.

That region is where the all important snowpack is formed. Snow typically stays frozen through the winter and then slowly dibbles out during warmer months to hydrate farms and cities when they need it most.

However, there's some concern that more precipitation will fall as rain instead of snow in the northern and central Sierras. That would do little to sustain the traditional water cycle California has historically depended on.

Cayan says though, if the 1982-83 and 1997-98 El Niño events are any indication, this winter should be relatively cool statewide, boosting the chances for snow.

Both those winters saw above average snowpack accumulation in the Sierras.

But she said state reservoirs are so low that even if some Sierra storms fall as rain rather than snow, that precipitation won't go to waste.

"So even if we get some warm storms, we are in such a state of deficit that water in any form is welcome," he said.