El Niño and Sonoma County water: the river, the reservoirs and your rain

By The Downspout · Posted Oct 12, 2026 · 6 min read

NOAA says a strong to very strong El Niño is likely this winter, which tilts California toward a wet one. On the Russian River, strong El Niño winters brought a major flood at Guerneville in 3 of 9 cases since 1951, about twice the usual rate, but the worst floods came in other winters. Get ready for high water and plan to keep some of the rain.

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Check the river now: Russian River level and forecast at Guerneville. Getting a house ready: winter storm checklist (Home Ready Sonoma).

Everyone in Sonoma County seems to have an El Niño story. The winter of 1983. The winter of 1998. This year has people asking if it is their turn again.

Here is what the forecasts say, what strong El Niños have done to the Russian River before, and what a wet winter could mean for the water we keep.

What El Niño is

Warm water, weak winds. About every 3 to 5 years, the ocean near the equator in the Pacific heats up and the winds that usually blow west die down.^[1]
Why it matters here. That shifts the jet stream and the storm track, which is why NOAA leans toward a wetter California winter.^[2]
The name. In Peru and along that coast, the warm current tended to show up near Christmas, and fish catches fell when it did. Fishermen named it El Niño, Spanish for "the boy," meaning the Christ child.^[1]
Its twin. La Niña flips it: the water cools and those winds blow harder.^[1]

Where El Niño stands

Strong and growing. As of October 8, 2026, NOAA puts the chance of a strong to very strong El Niño through January to March 2027 above 83%.^[3]
Maybe the biggest yet. NOAA says it could beat every El Niño on record back to 1950.^[3] By July to September it was already warmer than 1997 at the same point in the year.^[4]
A wetter tilt. NOAA's winter outlook gives California up to a 50 to 60% chance of above normal precipitation near the coast from December through April.^[2]
Weaker pull up north. Southern California has a stronger chance of a wet El Niño winter than the north, and the effect is usually strongest in late winter.^[5] Only half of six strong El Niños on record by 2015 brought above normal rain statewide.^[6] For the rest of the state, region by region, see Home Ready California's El Niño guide.
Officials are not waiting. The Governor declared a statewide emergency on September 21.^[7] Sonoma County declared its own on October 6 and is clearing culverts and flood channels and getting rain, stream and reservoir monitoring ready.^[8]

What strong El Niños did to the Russian River

We lined up NOAA's El Niño record with every crest the weather service lists for the Russian River at Guerneville, for the 75 winters from 1951 to 2025.^[4]^[9]

Our calculation from NOAA ONI and National Weather Service crest data. Method: a winter counts as strong El Niño if its November to January or December to February ONI is 1.5 or more; each winter is then counted if its highest crest reached 40 feet. A winter with no crest in the list is not counted as a flood.

Strong El Niño winters brought a major flood about twice as often as winters overall: 3 of 9, against 13 of 75.
But the six highest crests since 1951 all came in other winters, including the 49.5 foot record of February 1986.^[9]
The last three strong El Niños stayed below flood stage at Guerneville.^[9]^[10]
Nine winters is a small sample. One more flood or one fewer changes the share a lot.

Strong El Niño winter	Highest crest at Guerneville	Result
1957-58	40.2 ft	Major flood
1965-66	42.5 ft	Major flood
1972-73	37.9 ft	Flood
1982-83	40.4 ft	Major flood
1991-92	not in the NWS list	No crest listed
1997-98	36.6 ft	Flood
2009-10	27.53 ft	Below flood stage
2015-16	26.72 ft	Below flood stage
2023-24	28.91 ft	Below flood stage

Highest listed crest in each water year (October to September). Flood stage is 32 feet, major flood 40 feet.^[9] 2023-24 from the river forecast center's recent peaks.^[10] For every major flood since 1940, see how the Russian River works.

What a wet winter means for the reservoirs

Map: Natural Earth. Sizes and the West Coast share from NOAA.

Pool sizes and who controls releases from CW3E. Not to scale.

Rivers in the sky. An atmospheric river is a long stream of water vapor in the sky, 250 to 375 miles wide.^[11]
A few storms bring much of the rain. Atmospheric rivers bring 40 to 50% of the rain in the Russian River basin, much of it in just a few storms a year.^[12]
Two jobs, one lake. At Lake Mendocino, Sonoma Water controls releases from the water supply pool. Above it, the U.S. Army Corps of Engineers runs releases for flood control.^[12]
Forecasts help keep water. The lake was the first test of Forecast Informed Reservoir Operations: using better storm forecasts to decide how much water to hold and when to let it go.^[12] A big El Niño winter will put that to the test.
Summer depends on winter. Under the 2026 state order, whether a year counts as Normal or Dry for river flows depends on how much water is in Lake Mendocino. See how the Russian River works and Sonoma Water's request to lower 2027 river flows.

Keep some of it

A wet winter is the best chance in years to store water in the ground and in tanks. Our view: catch what you can, and slow the rest down.

Soak it in. Rain that sinks into a yard refills soil and, in the right spots, groundwater. See can your yard recharge groundwater and sink it or shed it, which also covers when to drain water away instead.
Catch it. Work out what your roof collects with the rain catch calculator, and size storage with the tank calculator.
Keep it clean. Storms wash whatever is on the street into creeks. Only rain down the storm drain.

What it means for you

Expect a wet winter, but do not count on one. El Niño shifts the odds.
If you live near the river, watch the Guerneville forecast and get your house ready now. Our sister site Home Ready Sonoma has an El Niño guide for Sonoma County homes.
Fix gutters and downspouts before the first big storm, and send the water somewhere it can soak in.
We will update this page as NOAA's forecasts change.