Water & Drought

New forecast says El Niño could help Northern California, ease drought

From left, Dominic Smith, Aiden Shephard  and Blake Machado,  all age 14 and of El Dorado Hills, wade to shore around rocks exposed by the American River’s low water level near the Rainbow Bridge in Folsom earlier this summer.
From left, Dominic Smith, Aiden Shephard and Blake Machado, all age 14 and of El Dorado Hills, wade to shore around rocks exposed by the American River’s low water level near the Rainbow Bridge in Folsom earlier this summer. pkitagaki@sacbee.com

El Niño might put a dent in the drought after all.

In a revised forecast Thursday, the National Weather Service said Northern California stands a decent chance of getting significant precipitation from this winter’s El Niño weather pattern, a development that could help ease the state’s four-year drought.

Until now, forecasters have been saying this winter likely would bring heavy rains to Southern California, which is typical for El Niño, but they’ve been less certain about the outlook for the northern half of the state. Because the state’s major reservoirs are in the north, that’s where the rain and snow need to fall to substantially bolster the state’s water supplies.

Michelle Mead, a forecaster in the agency’s Sacramento office, said Sacramento and the Sacramento Valley have at least an 80 percent chance of seeing average precipitation this winter. The chance of above-average precipitation has been pegged at 34 percent to 40 percent, she said.

“Not that it will be a deluge and everybody needs to stop conserving water,” she said. The bulk of the precipitation will fall in December, January and February, she said.

William Patzert, a climate expert at NASA’s Jet Propulsion Laboratory in Pasadena, was less circumspect, saying he’s convinced El Niño will be felt in Northern California. “At this point – at this particular time – this is too large too fail,” he said. “People like to be conservative. They don’t want to stick their neck out. But this is definitely the real deal.”

If history is a guide, California will see big snow in the northern mountains along with rain in the south, Patzert said. “The last two El Niños that were of this magnitude hosed all of California,” he said. “If you look at the snowpack for those two El Niños, you had double the snowpack, too.”

What’s changed since the weather service’s previous forecasts? Mead said analysts took a fresh look at previous winters and concluded that strong El Niños tend to bring heavy rains in the north. Other forecasters noted the persistence of this year’s El Niño and said temperature anomalies in the South Pacific are favorable to Northern California’s rain outlook.

“Moderate El Niños tend to get Southern California wet, and the strong ones get all of California wet,” said Jeffrey Mount, a water specialist at the Public Policy Institute of California. Mount said he’s encouraged that the so-called “ridiculously resilient ridge,” the high-pressure system that kept rain and snow from falling on California, is breaking down.

But Mount and Jay Lund, an engineer and watershed specialist at UC Davis, noted that the relative scarcity of strong El Niños – just six since 1957 – means it’s difficult to get too comfortable with the latest forecast.

“We have a small sample size,” Lund said. “There’s still a substantial probability that we’re going to be in a drought next year.”

State climatologist Michael Anderson, who has urged caution as El Niño fever has risen in the last few months, said he, too, thinks there’s a better chance of significant precipitation in Northern California. “As we get closer, we are seeing trajectories move in a more favorable outcome,” he said.

Anderson nonetheless encouraged Sacramento residents to continue to conserve water. He and others noted that the drought is so severe that even a huge rainfall year will not fully erase its effects. Plus, he said, “We want to wait until we actually see it.”

Mead said Sacramento received 13.8 inches of rain last winter, about 68 percent of average.

El Niño is a phenomenon linked to above-average water temperatures in the Pacific Ocean. Mead said the temperature is expected to peak at 2.5 degrees Celsius above normal this winter, ranking this among the strongest El Niños on record.

The latest forecast put the chance of El Niño striking at 95 percent, the same as a month ago.

Dale Kasler: 916-321-1066, @dakasler

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