La Niña Could Make California's Wild Weather Year Stranger

Storm-battered California is still in the grip of a wet El Niño winter, but in an unexpected plot twist, La Niña could be hot on its heels.

The El Niño-La Niña Southern Oscillation, or ENSO, is a weather pattern in the tropical Pacific that can influence weather around the world and throughout the Golden State, although its results are never guaranteed.

Typically, El Niño is associated with warm, wet winters in Southern California, while La Niña is associated with colder, drier conditions.

So far this year, El Niño has kept that promise. The pattern intensified in recent months, becoming what is now believed to be the fifth-strongest El Niño on record, according to an advisory issued this week by the National Oceanic and Atmospheric Administration.

Since December, California has been hit by intense atmospheric rivers, including three storms that brought record rainfall in Oxnard, San Diego and Los Angeles. The latest storm killed at least nine people and caused mudslides, debris flows and two tornadoes.

But California's wild weather may not be over yet, as there is now a 55% chance that La Niña will develop sometime between June and August, the advisory says. There is a 77% chance that it will develop between September and November.

A Beverly Crest home that was torn from its foundation by a landslide when an atmospheric river unleashed heavy rains in Southern California this week.

(Allen J. Schaben/Los Angeles Times)

“We look at a lot of state-of-the-art climate models, and there's a lot of consensus among them that we will potentially transition to La Niña,” said Michelle L'Heureux, a climate scientist at the NOAA Climate Center. Prediction Center. “Collectively, that's why we issued the watch.”

La Niña tends to favor the opposite pattern of El Niño, L'Heureux said. During La Niña, the central and eastern Pacific Ocean cools and the jet stream (the river of air that moves storms eastward around the world) shifts north. Basically, the effect creates a big ridge in the northern Pacific Ocean, which “can help dry things out across the entire southern panhandle of the United States, and that includes California,” he said.

L'Heureux cautioned that it is still too early in the year to make predictions about how the next winter might play out in California. ENSO is more of a “big nudge” that encourages climate systems to reappear along a certain preferred pathway, rather than a guaranteed outcome.

“It's not a disaster yet,” he said of La Niña. “There is still a 1 in 4 chance of this not happening, and seeing that progress will be important to say something about the impacts. Because once it emerges, we can be a little more confident in certain impacts.”

TO Rare three-year streak of La Niña between 2020 and 2023 was a notable factor in California's most recent drought, which led to unprecedented water restrictions, a decline in groundwater supplies and record levels in the Colorado River.

If the latest forecast is confirmed, the West Coast could once again experience a rapid shift from precipitation to dryness, a pattern sometimes referred to as “climate whiplash” and that is becoming increasingly common in a world that is heats up.

In fact, El Niño and La Niña do not act alone. Climate change is also exerting a greater influence on conditions in California and the United States, and there is a “constant interaction” between ENSO and global warming, L'Heureux said.

“There will always be a push provided by El Niño and La Niña, but there will also be a push provided by climate change,” he said.

Bill Siples installs chains on the tires of a motorist heading to Big Bear on State Highway 330 while it was snowing in the region Tuesday.

(Robert Gauthier/Los Angeles Times)

That could translate to heavier rainfall during El Niño years, he said, not unlike the conditions experienced in Los Angeles this week. In the case of La Niña, that could mean more evaporation, more heat and more extreme droughts due to warmer conditions.

What's more, there are other weather patterns that can influence California's climate that are not predictable at this time of year, such as the Madden-Julian oscillation, a fast-moving phenomenon in the central tropical Pacific that develops on a scale of subseasonal time. . Random weather phenomena are also not predictable so far.

What all this means for California's water supply remains to be seen.

As of this week, recent storms have filled the state's largest reservoirs to 118% of their historical average. Statewide precipitation is 102% of average for the date, with more than 13 inches falling since the start of the water year on Oct. 1, according to state data.

But most of the moisture has fallen in Southern California, and mostly in the form of rain, leaving some California Department of Water Resources officials concerned about a “snow drought.” The slow and steady melting of the Sierra Nevada snowpack each spring and summer has long been a key component of the state's water supply.

Last year, the Sierra was hit by intense cold storms that generated a near-record snowpack: 237% of normal on April 1, when it is normally at its peak.

The latest round of storms provided a boost, increasing the snowpack to 76% of average for the date, up from 50% on January 31.

However, the Sierra snowpack remains only halfway to its April 1 peak, “so if we see a longer period of dry conditions it is still possible to end the season with snowpack below average,” said Michael Anderson, DWR state climatologist.

“While climate factors like El Niño or La Niña change large-scale weather patterns that impact the Northern Hemisphere, each year California's water supply and risk of floods or droughts are driven by the timing, pace and the scale of atmospheric river storms,” ​​Anderson said. . “When we miss these storms and have more warm, dry days in winter caused by climate change, we start to slide into drought. “If storms are too large, come too quickly one after another, or persist, then flooding conditions arise.”

DWR is working with federal, state and local partners to improve its seasonal forecasting capabilities, Anderson said. But it is also important to continue investing in other water management strategies, such as stormwater capture, groundwater recharge, and recycled water, to ensure water supply reliability.

“It is up to us as water managers to capture and store as much water as possible during wet times like the ones we are seeing now, because we never know when drought conditions will return,” he said.

The forecasts for the rest of the winter remain somewhat ambiguous. Above average temperatures are favored in the state through April, while above average precipitation is favored only in Southern California.

What's more, the strong El Niño appears to have passed its peak, L'Heureux said.

He added that it is not uncommon for a strong El Niño to give way to La Niña, which occurs in approximately 60% of historical cases.

Gavin Schmidt, director of NASA's Goddard Institute for Space Studies, similarly said it's not unusual to swing back and forth in ENSO.

“However,” he said, “the predictability of the winter time pattern at this point in the year is not very slick, so I would be wary of any La Niña forecast until June/July or so.”