FrostList

When to Winterize Your Boat in Rohnert Park, CA

ON TRACK151 days until first 28°F freezeDec 9

Freeze protection for a Rohnert Park boat keys off the first 28°F freeze, which averages December 9, so haul out and winterize by December 2 to beat it. The early-to-late range spans roughly 53 days, so treat the median as a midpoint, not a promise.

OUTLOOK

Typical first first 28°F freeze near Dec 9; local deadline about Dec 2. The live 10-day outlook loads here.

Local freeze dates for Rohnert Park

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Nov 9Nov 25Dec 16
28°F (hard freeze)Nov 20Dec 9Jan 12
24°F (severe)Dec 1Dec 21Jan 12

NOAA station: Petaluma AP · 7.6 mi away · 20 ft elevation.

The reference station for Rohnert Park is Petaluma AP (7.6 mi, 20 ft). First freeze there: 32°F by Nov 25, 28°F by Dec 9, 24°F by Dec 21. That hard freeze has landed anywhere from Nov 20 to Jan 12, a swing of roughly 53 days. Spring's last 32°F freeze clears around Feb 28.

Expect the first frost near Nov 25 in Rohnert Park and the first hard freeze by about Dec 9. The 32°F date swings from Nov 9 at its earliest to Dec 16 at its latest, near 37 days. The last spring freeze averages Feb 28 and as late as Apr 6, which sets the safe window for reopening outdoor water and de-winterizing gear. Snow barely registers here; the freeze date, around Feb 28, is the one that matters.

Your boat checklist

  1. Change the engine oil and filter while the motor is warm so contaminants leave with the old oil.
  2. Run the engine on antifreeze until pink fluid reaches the outlet, protecting the block and manifolds.
    Helpful gear: Marine antifreeze — Recommended pick
  3. Fog the cylinders with fogging oil as the engine runs down to coat internal parts against corrosion.
    Helpful gear: Fogging oil — Recommended pick
  4. Top off the fuel tank and add stabilizer to limit condensation and protect ethanol-blend fuel.
    Helpful gear: Marine fuel stabilizer — Recommended pick
  5. Drain the raw-water system, the livewell, and any washdown lines that can trap water.
  6. Remove the battery, charge it fully, and keep it on a maintainer over the layup.
    Helpful gear: Battery maintainer — Recommended pick
  7. Support the cover so snow and rain shed off, and leave vents so the interior can breathe.
  8. For an inboard or sterndrive, follow the manual closely — those blocks are the ones freeze claims hit hardest.

What to have on hand

Marine antifreeze
Propylene-glycol fluid rated for engine blocks and systems.
Recommended pick
Marine fuel stabilizer
Additive that protects ethanol-blend fuel over the layup.
Recommended pick
Fogging oil
Spray that coats cylinders against corrosion in storage.
Recommended pick
Battery maintainer
Keeps the cranking battery topped off on the trailer.
Recommended pick

What this means locally

Compared with nearby cities, Rohnert Park's first-freeze date near Dec 9 sits about a week ahead of Santa Rosa (Dec 16) and close to Petaluma (Dec 9). California's deadlines span Jan 9 to Dec 30 statewide — one date for all of California would be off by weeks for Rohnert Park. Once you know Rohnert Park's freeze date, use it to winterize an RV and store a motorcycle too.

Other winter jobs in Rohnert Park

Every task below is dated to Rohnert Park's own freeze and snow normals.

Sprinklers → Nov 29Frozen pipes → Nov 9Car battery → Dec 9Sump pump → Feb 28RV → Nov 29Motorcycle → Nov 25

See the full Rohnert Park winter checklist, in order →

Frequently asked questions

At what temperature does a boat engine block crack?
Trapped water in an engine block or manifold can freeze and crack the casting once temperatures fall below 32°F and stay there long enough. Inboard and sterndrive blocks hold the most water and are the most vulnerable. Draining fully and adding antifreeze before the first hard freeze near Dec 9 is the protection.
Do outboards need winterizing?
Yes. An outboard should be drained so no water sits in the powerhead or lower unit, and the fuel system stabilized. Outboards self-drain better than inboards when tilted down, but fogging the cylinders and changing the gear oil are still part of a proper layup.
Fogging oil: is it necessary?
Fogging coats the cylinder walls and internal parts with a film that resists corrosion during months of storage. On engines that sit all winter it is cheap insurance against rust, especially in humid or coastal storage. Follow your engine maker's guidance on how to apply it.
How much does boat winterization cost?
A professional winterization varies with engine type and boat size, and inboards cost more than a simple outboard. Doing it yourself costs mainly antifreeze, oil, and fogging oil. Either way, the bill is far smaller than repairing a cracked block, which is the failure winterizing prevents.
Do boats in CA really need winterizing?
If temperatures reach freezing where the boat is stored, yes. Freeze claims are common in milder states precisely because owners assume they are safe and skip the step, then a rare cold snap cracks a block. Check the local freeze dates above and protect the engine before the first hard freeze.
When should I de-winterize my boat?
De-winterize in spring once the risk of a hard freeze has passed for your area. Reconnect and charge the battery, replace drain plugs, check hoses and clamps, and inspect the fuel system before the first launch. Reopening too early leaves the block exposed to a late cold snap.

Data: NOAA 1991–2020 normals via Petaluma AP, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.