FrostList

When to Winterize Your Boat in Florissant, MO

ON TRACK125 days until first 28°F freezeNov 13

The first 28°F freeze near Florissant averages November 13 (1991–2020 normals) — enough to crack an unprotected block even where owners assume they're safe — so winterize the boat by November 6. Year to year the date swings about 28 days, which is why the live outlook beats the calendar.

OUTLOOK

Typical first first 28°F freeze near Nov 13; local deadline about Nov 6. The live 10-day outlook loads here.

Local freeze dates for Florissant

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Oct 23Nov 4Nov 18
28°F (hard freeze)Nov 2Nov 13Nov 30
24°F (severe)Nov 8Nov 24Dec 11

NOAA station: St Louis Lambert Intl AP · 3.7 mi away · 531 ft elevation.

Numbers for Florissant come from St Louis Lambert Intl AP, 3.7 miles away at 531 feet, where the medians fall 32°F by Nov 4, 28°F by Nov 13, 24°F by Nov 24. The 28°F freeze has come as early as Nov 2 and as late as Nov 30, a 28-day spread. Spring's last 32°F freeze clears around Apr 2. Snowfall averages 17 inches a year, first reaching an inch near December.

In Florissant, freezing nights (32°F) typically begin around Nov 4 and the first hard freeze (28°F) follows near Nov 13. Year to year, the first 32°F night has fallen anywhere from Oct 23 to Nov 18 — about 26 days apart. Spring's final freeze lands near Apr 2 and as late as Apr 17, so that is when outdoor water and stored gear can safely come back online. Snowfall averages roughly 17 inches a year — enough that a working snow blower and a clear roof edge earn their keep.

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, Florissant's first-freeze date near Nov 13 sits close to St. Charles (Nov 10) and close to St. Louis (Nov 15). Missouri's deadlines span Oct 19 to Nov 8 statewide — one date for all of Missouri would be off by weeks for Florissant. Once you know Florissant's freeze date, use it to winterize an RV and store a motorcycle too.

Other winter jobs in Florissant

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

Sprinklers → Nov 3Frozen pipes → Oct 23Ice dams → Nov 15Car battery → Nov 13Snow blower → Nov 24Sump pump → Apr 2RV → Nov 3Motorcycle → Nov 4

See the full Florissant 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 Nov 13 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 MO 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 St Louis Lambert Intl AP, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.