La Niña Watch: Just how wet will San Francisco get?

As the Bay Area bakes under summer’s heat, small changes in the Pacific Ocean signal a shift in the weather — and it could mean a better chance for a drier, warmer winter in The City after some recent years of above-average precipitation .

Climate models now predict a two-in-three chance of a La Niña pattern forming later this year, with the probability increasing for La Niña to persist into the winter months.

According to the Climate Prediction Center’s latest discussion , such conditions are “favored to emerge during September-November (66% chance) and persist through the Northern Hemisphere winter 2024-25 (74% chance during November-January).”

Historically, the La Niña pattern has more often brought below-average rainfall to Northern California. And while it might be nice to have fewer days carrying umbrellas or wearing galoshes, the state still teeters on the edge of drought , highlighting how fickle the Golden State’s climate can be.

While La Niña tilts the odds toward drier conditions, it doesn’t guarantee them.

During the recent La Niña in the 2020-21 water year, San Francisco received only 9 inches of precipitation, one of the driest years on record. Yet during another La Niña year in 2016-17, The City received an above-average 32 inches of rainfall, illustrating the variability of La Niña’s impact.

El Niño and La Niña are opposite phases of a natural climate pattern called the El Niño-Southern Oscillation. The ENSO phases are driven by shifts in the temperature of the ocean’s surface waters in the equatorial Pacific, with far-reaching effects on global weather.

During El Niño, warmer-than-average waters spread across the central and eastern Pacific, disrupting typical wind patterns. This can lead to wetter conditions in some regions — like the southern U.S. — and drier conditions in others, such as Southeast Asia and Australia.

La Niña, on the other hand, brings cooler-than-average waters to the same region. This intensifies the trade winds that blow from east to west, pushing warm surface waters toward Asia and allowing cooler, nutrient-rich water from the ocean depths to rise along the eastern Pacific. These shifts in ocean temperatures alter the atmosphere above, leading to global weather patterns that often bring drier conditions to Northern California.

“ENSO-neutral conditions persist in the western equatorial Pacific,” according to the latest ENSO Forecast from this month. The report noted that “borderline La Niña conditions are forecasted during Oct-Dec, and Nov-Jan, but with very weakly elevated probabilities.”

It also highlighted that “ENSO-neutral conditions subsequently re-emerge as the most likely during the boreal winter and spring of 2025.”

Right now, the Pacific Ocean’s surface temperatures remain near average, signaling an “ENSO-neutral” state, meaning the waters are neither warmer nor colder than usual. But beneath the surface, cooler waters are spreading — a typical precursor to La Niña. Coupled with stronger-than-normal easterly trade winds, these conditions suggest that La Niña is indeed on the horizon.