California’s El Niño Winter Could Be ‘Profoundly Unsubtle,’ Scientists Warn
The odds of an unusually wet winter in the Bay Area are rising as El Niño continues to strengthen, according to climate scientist Daniel Swain.
The UC Agriculture and Natural Resources researcher said that statewide, there’s a “90% to 95% confidence in a wetter-than-average winter,” with the biggest spike most likely to come in January and February.
“It’s walking like an El Niño, and it’s talking like an El Niño,” Swain said during a virtual office hours session on Tuesday. “So far, it is all systems go.”
Swain’s “high-key level takeaway” is that October El Niño updates show the likelihood of California-related impacts increasing “from already pretty high confidence” in September.
Swain said all 10 of the major models “are singing roughly the same tune” about precipitation possibilities.
“The Bay Area and the North Bay in particular, all the watersheds there, are more likely to see very wet conditions this winter than not,” Swain said.
In his most recent blog post, Swain said that El Niño will likely strengthen for up to two months before peaking between November and January. But he said that impacts are often delayed to “the peak intensity” of El Niño itself, and “This is likely to be true in California.
“This year’s tilt in the odds toward wet and stormy conditions in California will be profoundly unsubtle,” Swain said.
Impacts could include torrential downpours, rain instead of snow events, flooding, temporarily elevated sea levels, severe thunderstorms and even “isolated tornadoes.
“This might be another winter, but on steroids,” Swain said. “This might be a year when the Hollywood version of bad weather in California actually ends up coming true.”
On the Sierra Nevada snowpack and how it might fare this winter, Swain said lower elevations could get more rain than snow, and that higher elevations of 8,000 feet or taller will likely have “a very snowy winter.” Swain said it could spell rain in South Lake Tahoe “almost all winter,” and that “there could be an enormous amount of snow up at the top of the Heavenly chairlift.
“I wouldn’t count on November or December in the Sierra Nevada [for snow],” Swain said. “The odds might get a little bit better as we go toward the back end of the season, and El Niño starts to lose its maturity.”
El Niño also produces massive Kelvin waves — when tropical trade winds slow or reverse. Swain said they have “completely reversed direction” — allowing warm water to push toward South America.
That water splits north and south when it hits land. A Kelvin wave has already swept along the coast, raising sea levels by more than a foot, along with thermal expansion also caused by El Niño. Another coastally trapped wave is also moving up the coast, but won’t reach California for around three weeks.
Swain is worried that major flooding could occur later this winter with king tides during Thanksgiving week and Christmas.
“This could be a big problem with disruption of transportation on major highways and interstates throughout California that run through low-lying coastal areas,” Swain said. “If there’s a major storm, we could see major or even record-breaking coastal flooding, and it wouldn’t even take an extreme storm.”