The likelihood this winter of an El Niño — the weather pattern marked by warm Pacific Ocean waters that can affect California’s rainfall — is increasing.
But so far, this El Niño looks more like a lamb than a lion.
The probability of El Niño conditions being present by December is now 70 to 75 percent, up from 50 percent five months ago, according toa new report Thursday from the National Oceanic and Atmospheric Administration.That doesn’t necessarily mean a wet winter.
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Ocean surface temperatures off South America, a key indicator, are only moderately warmer than historic averages. That’s leading scientists to characterize this year’s event so far as a weak El Niño. In other words, don’t break out the umbrellas just yet.
Historically in California, similarly weak El Niño years have brought just as many below-average rainfall winters as above-average ones.
“Weaker types of events — which is what we anticipate here — have a weak precipitation signal for California,” said Mike Halpert, deputy director of NOAA’s Climate Prediction Center in College Park, Maryland. “We don’t expect this event to be strong enough to give us the confidence to favor a wet winter. Right now there’s an equal chance of below normal, normal, and above normal rainfall.”
Many people think El Niño conditions are a near-guarantee of wet winters in California. But that’s not the case. Generally speaking, the warmer the ocean temperatures are near the equator during El Niño years, the greater the likelihood of heavy winter rains in California.
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Since 1951, there have been 17 winters with a weak or moderate El Niño conditions. During those, both the Bay Area and the Los Angeles area experienced below-normal rainfall totals in seven winters, average rainfall in four and above-normal rainfall in the other six, according to studies by Saratoga meteorologist Jan Null.
“We don’t know what it means for rainfall,” Null said. “We’ve seen way too much variation with weak events to draw a conclusion. As we learn more and more about El Niño events, there is no one-size-fits-all answer like ‘El Niño means lots of rain for California,’ which was the conventional wisdom in the 1980s and 1990s.”
Stronger El Niño conditions have meant a greater chance — but not a guarantee — of wet winters.
The three strongest El Niño winters in California since 1951 saw drenching, relentless storms and flooding twice, in 1982-83 and 1997-98. But the same strong conditions in the most recent one, the winter of 2015-16, disappointed millions of people.
That year, despite El Niño conditions so strong that one Southern California scientist referred to them as “Godzilla,” rainfall totals ended up at 95 percent of normal in the Bay Area, and 72 percent of normal in the Los Angeles basin, dashing hopes then that the five-year-drought would be broken. There were big wet storms, but Oregon and Washington received the brunt of the rain and snow that winter.
Ironically, the following year, during weak La Niña conditions in the winter of 2016-17, when ocean waters were cooler than the historic average, massive storms finally ended California’s drought. They delivered record snowfall so deep that some Sierra Nevada ski resorts had to temporarily close. They also caused major flooding on Coyote Creek in downtown San Jose, wrecked Highway 1 in Big Sur and the spillway at Oroville Dam, and filled reservoirs across the state.
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Currently, in large part because of those storms nearly two years ago, reservoir conditions remain in decent shape, with the largest reservoirs in California at 105 percent of their historical average on Thursday morning, slightly above normal for mid-October. That’s why there have been virtually no water use restrictions this summer in many parts of the state.
But California needs more rain.
Overall, 48 percent of California was classified Thursday as being in moderate drought conditions or stronger, according to federal scientists, up from 8 percent last October.
The Bay Area and Monterey Bay region are not considered to be in a drought. But Santa Barbara to San Diego is, as is the San Joaquin Valley and the Southern California desert,according to the U.S. Drought Monitor, a weekly report.
The term El Niño — or “little boy” in Spanish –- was originally used by fishermen off Ecuador and Peru to refer to “the Christ child” because warming ocean conditions appeared around Christmas every three to eight years.
The opposite, or cooling ocean water, is a “La Niña.”
With each month that draws closer to California’s winter rainy season, forecasts become more reliable.
Halpert, at NOAA, said based on computer models from weather agencies around the world, it looks like the warmer ocean waters will peak in December or January, at about 1.8 degrees Fahrenheit above the historic average. That would put this El Niño right on the boundary between weak and moderate.
“None of the models are predicting this to be one of the real strong ones,” he said. “If I were hoping for a wet winter in California this year, I would try to temper my enthusiasm. It could easily be dry as wet.”
Distributed by Tribune Content Agency
