It’s understandable that Californians are confused by weather forecasts.
Scientists announced in October that La Niña had arrived, and many associate it with dry conditions, especially in the south.
But, at least for now, we’re experiencing a very wet season, with rain bringing much-needed moisture to the brush, perhaps ending the fall fire season, and helping to keep the state’s reservoirs in good condition.
So what’s going on?
La Niña is still real there is a tendency This correlates to a dry year, which the National Weather Service defines as October 1st to September 30th.
sea surface temperatures in the central and eastern Pacific Ocean are lower. The jet stream (a band of west-to-east winds in the atmosphere) then moves north. This typically pushes winter storms toward the Pacific Northwest and Canada, leaving some areas of California, especially the south, drier than average.
Of the 25 La Niña events since 1954, 15 have brought drier-than-normal conditions to California.
But La Niña “doesn’t necessarily mean drought,” said meteorologist Jean Null, an adjunct professor at San Jose State University.
In fact, of the seven La Niña events observed in the past 15 years, three of them have been incredibly rainy.
Powerful storms hit California in 2010 and 2011, forming snowpack and destroying ski resorts.
The 2016-17 La Niña season brought 134% of the average annual precipitation to downtown Los Angeles. This was the highest precipitation total in the entire state and single-handedly ended California’s punishing five-year drought.
There was so much rain that season that Lake Oroville, California’s second largest reservoir, spilled over its rim. Massive evacuations were ordered amid fears it would collapse and flood the area below, but the tragedy was ultimately averted.
But in San Jose, coyotes have come out of Creek and invaded many homes. The snowfall is so heavy that in June skiers were descending the slopes of the Sierra Nevada in their underwear.
The 2022-23 La Niña season is yet another drought, marking the end of California’s drought on record. That rainy season caused landslides in the summer of 2023 that destroyed eight homes. It also helped accelerate land displacement in the Portuguese Bend neighborhood of Ranchos Palos Verdes, cutting off service to dozens of homes, public works shutting down more than 100 homes and prompting hardship for Beloved, a national historic landmark and popular wedding venue.
Still, Californians who lived through the 1980s and ’90s tend to think of La Niña and its better-known counterpart, El Niño, in absolute terms. The former is seemingly “”, and the latter looks like a harbinger of epic rain and floods.
The truth is that La Niña and El Niño are by no means the only factors predicting weather patterns heading into California’s fall and winter rain and snow seasons.
“Forecasting El Niño/La Niña is like poker: You might have a good hand, but when you draw the last card, you don’t get what you’re looking for,” said Marty Ralph, director of the Western Weather and Water Extremes Center at Scripps Institution of Oceanography at the University of California, San Diego.
During El Niño events, sea surface temperatures increase in the central and eastern Pacific Ocean. The jet stream could move south and release moisture with fire hoses, directly reaching California, especially the southern part of the state.
“During the ’80s and ’90s, we saw a really good correspondence between El Niño/La Niña events in precipitation anomalies in Southern California, where we had wet El Niños and dry La Niñas,” Ralph said. “But interestingly, when we switched to the 21st century, somehow something changed.”
Some El Niño events are out of character for California. The most recorded El Niño event occurred in downtown Los Angeles in 2006-2007. And the 2015-2016 water year was preceded by El Niño, which brought below-average winters to both Southern and Northern California despite the ocean’s mighty power.
Ralph and his colleagues sought to understand why certain La Niña and El Niño water years were what they called “heresy,” behavior that deviated “significantly” from their expectations.
What they found was that La Niña and El Niño are more likely to influence certain storms that hit California. However, Ralph said it’s just a typical seasonal phenomenon originating from Alaska or northern Hawaii.
But what La Niña and El Niño don’t affect are the “atmospheric rivers” that can carry large amounts of rain and snow from the tropics to California, Ralph said. The findings were reported in the journal February.
Each river in the atmosphere can carry enough water to fill a ship. In just four to five days, Ralph said, Southern California will have an average rainy season. Atmospheric rivers drove the powerful storms that hit California this year and this year.
According to the American Weather Society, the average atmospheric river carries more than twice the flow of the Amazon River.
On average, atmospheric rivers account for up to 65% of Northern California’s annual precipitation. But atmospheric rivers contribute between 5% and 71% of Southern California’s annual precipitation, which can vary widely from year to year, according to the report.
Also, whether climate change will overturn the old rules of La Niña and El Niño events merits further study. That’s because atmospheric rivers are “projected to contribute increasingly to total annual precipitation, increasing precipitation extremes and increasing interannual variability in Western hydroclimate in a warming future,” the researchers wrote.
Officials have long warned that continued climate change could send California into a tumultuous period of extreme precipitation, with the state becoming drier and interspersed with exceptionally wet years.
“La Niña and El Niño are not the only factors in this game,” Null said. “I think we need to add an appendix to that strategy. Part of that is due to climate change. … Climate change is in the DNA of every weather phenomenon that’s happening right now.”
California has seen unusually wet storms this fall due to a low-pressure system off the West Coast that extends further south than usual in October and November. John Gottschalk, director of the operational prediction division at the National Oceanic and Atmospheric Administration’s Climate Prediction Center, said the system was able to take advantage of unusually strong precipitation deep in the tropics and send atmospheric river storms into the state.
Santa Barbara Airport has recorded the wettest start of the year so far with 9.91 inches of rain, surpassing the National Weather Service’s previous record of 7 inches in Oxnard.
Since Oct. 1, UCLA has gained 8.75 inches and downtown Los Angeles has gained 6.94 inches, about half of the average annual total.
Even in the notoriously dry Death Valley National Park, November was the wettest on record, exceeding the 1923 high water mark with 1.76 inches, said Chris Outler, a meteorologist at the National Weather Service office in Las Vegas.
Las Vegas had the second-wettest September, October, and November of this year, with 2.91 inches of precipitation.
Rainfall across Southern California was relatively high for this time of year, enough to greatly reduce the risk of wildfires, but not enough to cause catastrophic landslides.
“It’s kind of a Goldilocks AR,” Ralph said.
But what wasn’t ideal was how warm it was in California. Ski resorts are lamenting the lack of snow due to recent storms. California’s healthy annual water supply creates seasonal ice reservoirs in the mountains that man-made lakes can never compete with.
The same low-pressure system off the coast that helped fuel recent atmospheric rivers is also pushing air from areas of western and southwestern California. This is warmer than when air enters California from Alaska or Canada.
As a result, November temperatures were “incredibly above normal” across the West, Gottschalk said. “It rained in Northern California, but it was too warm,” he said.
Gottschalk said the early start of California’s rain and snow season doesn’t necessarily mean “it’s going to rain all winter long.” “That’s not going to work.”
Let’s take a look at the La Niña phenomenon for the 2021-22 season. It was the fourth wettest October in California history, thanks to the most damaging Category 5 atmospheric river. However, the following year, January to April was the driest period on record in California. By April 2022, California’s snowfall was only 38% of normal.
At this time, there are no significant rain or snowstorms forecast for California into early December.
“Recent history shows us what can happen in a California winter,” said Carla Nemeth, director of the California Department of Water Resources.
