El Niño flood prevention for Sonoma County homes, and the first hours after water gets in

El Niño 2026–27 · Updated October 18, 2026

Companion guides: flood prevention · roof prep · drying and mold timeline · North Bay Pros storm prep

Sonoma County has a long memory for floods: the Russian River's flood of record at Guerneville in February 1986, the February 2019 crest at 45.38 feet, and Petaluma's floods in 1982 and 2005. This guide covers what to do before the season, during a storm, and in the first hours if water gets in.

What NOAA is saying about this winter

NOAA's Climate Prediction Center (CPC) put an El Niño Advisory in effect, and its ENSO Diagnostic Discussion of October 8, 2026 says a strong-to-very strong El Niño is likely through January–March 2027, with better than an 83% chance. CPC is careful to add that, with an event this large, El Niño-type impacts are "larger, though not guaranteed." For Sonoma County, that means a wetter-than-normal winter is more likely, not certain. CPC's next update is due November 12, 2026.

The City of Sonoma is taking it seriously: it opened its sandbag filling station early this year because of the outlook, while noting that El Niño "does not guarantee" flooding or severe storms (City of Sonoma).

This week: three things that take an hour

1. Sign up for SoCoAlert. It's the County's free system for evacuation notices, shelter-in-place orders and flood warnings. Sign up online with up to five addresses, or call (707) 565-1369 (SoCoEmergency).
2. Look up your flood risk. Search your address on FEMA's Flood Map Service Center. Petaluma residents can also check the city's updated flood maps.
3. Check your insurance. Homeowners policies don't cover flooding, and a flood policy typically takes up to 30 days to start (SoCoEmergency).

Before the first big storm

• Clear gutters, downspouts and drains. The City of Sonoma asks residents to collect leaves rather than blowing them into the street, and to keep gutters and drainage areas clear (City of Sonoma).
• Extend downspouts so water lands well away from the foundation.
• Make sure soil slopes away from the house.
• Test your sump pump. SoCoEmergency suggests a sump pump with a battery and installing check valves (SoCoEmergency).
• Move valuables and important papers off floors in garages and lower levels.
• Know where your main water shutoff and electrical panel are.
• Build or refresh a go-bag. Ready.gov has a checklist.

Sandbags

Sandbags redirect shallow, moving water; they don't make a home waterproof. Sonoma County lists sandbag assembly stations during weather events on its sandbag page, and cities run their own. The City of Sonoma's self-serve station at Depot Park, 270 First St. W, opens October 20, 2026 for city residents (City of Sonoma), and Santa Rosa residents with a city ID can get sand and bags at 55 Stony Point Road during significant rain events (Santa Rosa Rain Ready). Locations change, so check the official page before you go, and bring a shovel. See our sandbag guide.

Know your river numbers

If you live near the lower Russian River, learn what the Guerneville gauge means for your street. Flood stage is 32 feet; at 35 feet the CNRFC expects numerous businesses and homes in the lowest parts of river towns to flood (CNRFC). Our Russian River flood stages guide has the full breakdown, including Healdsburg and the Laguna at Sebastopol.

During the storm

• Follow SoCoAlert and NWS Bay Area updates. Sonoma Water's Flood Forecast Hotline is (707) 526-4768 (Sonoma Water).
• Never walk or drive through floodwater: six inches of moving water can knock you down (SoCoEmergency).
• If you're trapped in a building, go to the highest level, but don't climb into a closed attic where rising water could trap you.
• Evacuate when told to.

If water gets in: hour by hour

Hour 0 to 1: Get people and pets safe. If you can reach the electrical panel from a dry spot, turn off power to wet areas. If it's floodwater, don't wade in. If it's a pipe, close the main valve.

Hour 1 to 3: Photograph and video every wet area and the water line on walls. Move what you can to dry ground. Call your insurer and a restoration provider.

Hour 3 to 24: Extraction starts. Wet carpet pad and soaked insulation usually come out. Drying equipment goes in.

Day 1 to 2: This is the window that matters for mold. The EPA says drying within 24 to 48 hours usually prevents it (EPA).

Day 3 and after: Daily moisture readings until dry, then repairs. Our sister site has a full drying and mold timeline, and our roofing site covers El Niño roof prep. The North Bay Pros storm-prep hub links all of our guides.

Hiring help after a storm

Verify any contractor at CSLB. In a declared disaster area, contracting without a license is a felony (CSLB).

Sources

• NOAA CPC ENSO Diagnostic Discussion, Oct 8 2026
• SoCoEmergency: Preparing for flood season
• SoCoEmergency: SoCoAlert
• SoCoAlert sign-up portal
• SoCoEmergency: Sandbags
• City of Sonoma: Planning ahead for winter weather (Oct 16 2026)
• City of Santa Rosa: Rain Ready
• CNRFC: Russian River at Guerneville
• Sonoma Water: Flood forecast & emergency information
• City of Petaluma: Flood management
• FEMA Flood Map Service Center
• Ready.gov: Build a kit
• EPA: A Brief Guide to Mold, Moisture and Your Home
• CSLB disaster guidance

Sources checked October 18, 2026.

Frequently asked questions

This page is general information, not legal, insurance or medical advice. Sources are linked in the text. Sonoma County Water Damage is a referral service and doesn't perform the work.