La Niña forecasts turned out to be all wet
The new year started off with a parade of storms, leading to San Francisco and the wider Bay Area seeing one of its rainiest time frames since the Gold Rush era.
This onslaught of storms seemed a bit out of place with the trend of La Niña, an outlook that traditionally brings warm, dry conditions to most of California. Instead, the first half of the 2022-23 winter season was marked by atmospheric-river-enhanced storms and notable reductions in drought conditions across the state. And chances persist for some rain showers to hit California in the coming days to weeks.
For meteorologists in both the Bay Area and across the Western U.S., this January’s shift toward wet and stormy conditions brings with it questions over what other factors might be stomping out the typical La Niña outlook. It also raises concerns over the flip to an El Niño pattern that longrange weather models are forecasting for the second half of the year.
Both El Niño and La Niña are two sides of the same coin, relating to the large-scale weather pattern that’s known as the El Niño-Southern Oscillation — or ENSO. This pattern is marked by a difference in water temperatures off the coast of South America.
During the El Niño phase, warmer-than-average waters over that part of the Pacific Ocean translate into more evaporation along the West Coast and eventually more low-pressure systems. In other words, storms bringing rain and snow are more likely to roll into California. During a La Niña phase, colder-thanaverage waters develop off the
“Most of all of the West right now — from California to Colorado — is well over 200% of normal” for its snowpack. Eric Boldt, meteorologist, National Weather Service
coast of South America, leading to less evaporation and drier conditions in California.
“Meteorologists have long been looking for (oscillations) that have longer timescales, months to years, and have a cyclical nature to them and have a significant influence over large areas,” said Warren Blier, National Weather Service Bay Area science and operations officer.
On paper, that makes sense. And both El Niño and La Niña have historically been used by meteorologists for finding cycles in the atmosphere that can be used for longrange forecasts. But given how much rain has fallen in just the last month, it’s hard to argue that La Niña had much of an influence on the West Coast’s weather patterns this winter season.
So, is the ENSO model broken? Not quite.
While El Niño or La Niña outlooks can shed some light on what the weather pattern across the thousands of miles between Japan and California might end up looking like for a winter season, other oscillations like the Pacific North American Oscillation are also at play.
In some years, the El Niño-Southern Oscillation is much stronger than in others, as was the case during the dry winters experienced during 2021 and 2022 La Niña years and the wet winter experienced in El Niño years in the early 2010s. During those years when the oscillation was at its strongest, meaning that there were huge deviations in average water temperatures off the coast of South America, the closed-system model worked like a charm.
Instead, the 2022-23 wet season has seen record-breaking rain and snowfall, more typical of an El Niño pattern.
“Most of all of the West right now — from California to Colorado — is well over 200% of normal” for its snowpack, said Eric Boldt, warning coordination meteorologist with the National Weather Service’s Los Angeles office.
If you imagine all the weather patterns as singers in a choir, then ENSO’s La Niña pattern sang so loudly in 2021 and 2022 that every other weather pattern in the atmosphere was lost in the noise. This year’s La Niña pattern has been much weaker than the last two years, and that’s allowed other weather patterns in the atmospheric choir to sing louder than La Niña.
“ENSO’s circulation is, to my mind, the most noteworthy of those (oscillations) that go out several months to a year or two,” Blier said. But while it only offers meteorologists a general picture of what conditions California can expect, “not what the high temperature or rainfall is going to be in San Francisco on some day, but the odds of how this season will play out.”
Meteorologists took notice of those other weather patterns at play back in September and October, which prompted raised conversations over the Pacific North American Oscillation’s influence on California’s winter weather outlook. Sure enough, its influence resulted in more low-pressure systems rolling into California from Hawaii by December and early January, culminating in the Pineapple Express-enhanced storms that drenched most of California.
So, why is ENSO so much less of an influence this winter?
After two long years of ENSO’s strong La Niña phase, it seems like the pattern is finally switching back to neutral. The Climate Prediction Center forecasts an 82% chance that ENSO will reach a neutral phase by spring. This lines up with the huge improvements in California’s drought monitor classifications over the past few weeks, with most of the state seeing anywhere from two to three categories of improvement.
These improvements have been seen across the state, with reservoirs seeing rainfall and snowfall that’s over 200% above the average for this time of the year across Northern and Southern California, all while the snowpack runs 400% higher than average at weather stations in the Sierra Nevada, like Kirkwood.
But even now, as La Niña begins to crank up the drier air and highpressure systems that you would expect to develop off the coast, the storm door is slated to remain open.
“We’re getting a break from the heavier rains, and then the rains that are starting to show up again as early as late this weekend and into the following weekend,” Boldt said, describing the chances for rain showers over the next few days. He also said that the systems bringing in these showers are “looking a lot colder and not as much moisture content overall, so these will be some lighter storm systems.”
As the La Niña phase continues to weaken this winter, storms will manage to fall through the cracks of an ENSO pattern that is set to go to neutral by spring. This means there won’t be a La Niña or El Niño pattern firmly in place over the Pacific Ocean.
Could El Niño return in 2023?
The long-range outlook on the global weather models paints some uncertainties over what may happen during the second half of 2023, with most suggesting that the neutral phase from this spring will evolve into an El Niño phase by fall.
Blier describes this shift between ENSO’s La Niña and El Niño phases as an atmospheric teetertotter. This means that after this spring’s neutral phase, the warmer-thanaverage waters off the coast of South America will add more weight on the teeter-totter, tilting the atmosphere toward an El Niño phase.
As opposed to zooming in on immediate impacts from La Niña and El Niño outlooks, it’s also important to consider what the broader implications of ENSO might be as weather systems travel from one side of the Pacific Ocean to another.
But while it only offers meteorologists a general picture of what conditions California can expect, “not what the high temperature or rainfall is going to be in San Francisco on some day, but the odds of how this season will play out,” Blier said.
With that being the case, then the West Coast will see one of two scenarios in its 2023-24 wet season that begins in October. It will either be an El Niño phase that promotes heavy rainfall and winter storms, or a short-lived El Niño phase that gets lost in the noise of all the other large-scale weather patterns and leaves California with light showers all winter long. Given the great improvements seen with the recent update of the drought monitor, this is looking like an optimistic outlook for the next wet season.