El Niño winter 2026-27: what it means for Sonoma County homes

What forecasters expect, what past strong El Niños did here, and what to do before the rain. Updated October 12, 2026.

The short answer. NOAA says a strong to very strong El Niño is likely through January to March 2027, with a better than 83% chance [1]. That tilts the odds toward a wet California winter, most of all near the coast [3]. It does not promise floods in Sonoma County. Get your house ready either way. Start with the storm checklist.

What El Niño is, and why it has that name

Every 3 to 5 years, the surface of the tropical Pacific runs warmer than average and the east winds there weaken [13].

That warm water shifts the jet stream and the storm track. NOAA's outlook ties this winter's wetter odds for California to those shifts [3].

Two maps of the Pacific Ocean with Sonoma County marked. In a normal year, trade winds blow west along the equator and warm water sits near Asia and Australia, with cooler water off South America. In an El Nino year the trade winds weaken, warmer than normal water spreads east along the equator toward South America, and the storm track shifts toward California. — Our drawing, based on NOAA's El Niño explainer and winter outlook. Coastlines simplified.

Why "El Niño"? Fishermen on South America's Pacific coast noticed the warm water often showed up around Christmas. They named it El Niño, Spanish for "the boy," after the Christ child [13].

La Niña is the opposite: cooler water and stronger east winds [13].

Where El Niño stands now

As of NOAA's October 8, 2026 update, El Niño is still strengthening [1].

The patch of the Pacific NOAA uses to measure it, called Niño-3.4, was 2.1°C above normal in September [1].

NOAA says this event could beat every El Niño on record back to 1950 [1].

Line chart of NOAA's Oceanic Nino Index by season. By July to September, 2026 was at 2.16 degrees above normal, ahead of 1997 at 1.79, 2015 at 1.73, 2023 at 1.25 and 1982 at 0.99. Those years peaked later between 1.99 and 2.59. — Values from NOAA's Oceanic Niño Index. Our comparison: the same July to September season in four past strong El Niño years, 1982, 1997, 2015 and 2023.

By July to September, this El Niño was already warmer than 1997 at the same point [2].

What forecasters expect this winter

Wetter odds, not a promise. NOAA's outlook gives California up to a 50 to 60% chance of above normal rain and snow near the coast from December through April [3].
The south gets the surer bet. Southern California has a stronger chance of a wet El Niño winter than Northern California [6].
Later is wetter. El Niño's pull on California rain is usually strongest in late winter, not early [6].
Not every strong El Niño delivers. Of six strong El Niños on record by 2015, only half brought above normal rain statewide: 1957-58, 1982-83 and 1997-98 [7].

What strong El Niños did to the Russian River

We matched NOAA's El Niño record with every big crest at Guerneville since 1951. The details are on our water site, The Downspout.

3 of 9 strong El Niño winters since 1951 brought a major flood at Guerneville: 1958, 1966 and 1983.
That is about twice the rate of all winters since 1951.
The last three strong El Niños, in 2010, 2016 and 2024, stayed below flood stage.
The six highest crests since 1951, including the 1986 record, came in other winters.

Two figures side by side. Strong El Nino winters: a major Russian River flood at Guerneville in 3 of 9, 33 percent. All winters since 1951: 13 of 75, 17 percent. — Our calculation from NOAA El Niño and river crest data, water years 1951 to 2025. Major flood: 40 feet or more at Guerneville. Method and full table on The Downspout.

So El Niño raises the odds. It does not decide them.

Satellite image of a long band of clouds and moisture stretching across the Pacific Ocean to California — A real atmospheric river reaching California on February 14, 2019, seen by NOAA's GOES-17 satellite. Image: NOAA.

A few atmospheric river storms bring much of the Russian River basin's rain each year [12]. They can come in any kind of winter.

What the state and county are doing

A road covered by brown floodwater, with a yellow road sign standing in the water — Never drive through floodwater. Turn around and find another way [4].

State, September 21. The Governor declared a statewide emergency to prepare for El Niño. The state is staging sandbags and pumps and has the National Guard ready for flood response [4].
County, October 6. Sonoma County declared its own emergency. Crews are clearing culverts and flood channels, checking places that have flooded or slid before, and staging sandbags [5].

"The best time to prepare for a flood is before a storm."
Rebecca Hermosillo, chair of the Sonoma County Board of Supervisors [5]

What to do before the rain

Work through the winter storm checklist. Gutters, downspouts, drains, trees and power.
Sign up for SoCoAlert with every phone in the house [9].
Look up your flood risk. Check your address on FEMA's flood maps [11]. The state also asks people to know if they live below a recent burn area [4].
Decide on flood insurance now. Most homeowners policies do not cover flood, and a new flood policy usually starts 30 days after you buy it [8].
Know your sandbag station. The county lists them during storms. Bring a shovel [10].
Plan your route out. Never drive through floodwater [4]. Check the county's road closures map before you drive.

What it means for you

Treat this as a likely wet winter, not a sure one.
Do the cheap work in October: gutters, downspouts, drains.
If you are near the river or a creek, sort out flood insurance and your way out now.
Check back. We will update this page as NOAA's forecasts change.

Winter storm checklist for Sonoma County homes

El Niño and Sonoma County water: the river, the reservoirs and your rain (The Downspout)

Storm Ready Plan

Sources

The chart is NOAA data compared by us. The Russian River flood counts are our calculation from NOAA data, explained on The Downspout. Forecasts change: last checked October 12, 2026.