FrostList

When to Winterize Your Boat in St. Louis, MO

ON TRACK127 days until first 28°F freezeNov 15

Freeze protection for a St. Louis boat keys off the first 28°F freeze, which averages November 15, so haul out and winterize by November 8 to beat it. The early-odds date runs roughly 13 days ahead of the median, so build in that buffer.

OUTLOOK

Typical first first 28°F freeze near Nov 15; local deadline about Nov 8. The live 10-day outlook loads here.

Local freeze dates for St. Louis

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Oct 24Nov 4Nov 21
28°F (hard freeze)Nov 2Nov 15Dec 4
24°F (severe)Nov 9Nov 26Dec 15

NOAA station: St Louis Sci Ctr · 3.9 mi away · 515 ft elevation.

For St. Louis, the nearest NOAA station with freeze data is St Louis Sci Ctr, 3.9 miles out at 515 feet. Median first-freeze dates there run 32°F by Nov 4, 28°F by Nov 15, 24°F by Nov 26. Year to year the 28°F date has ranged from Nov 2 to Dec 4 — about 32 days apart. Spring's last 32°F freeze clears around Apr 1. Snowfall averages 14 inches a year, first reaching an inch near December.

In St. Louis, freezing nights (32°F) typically begin around Nov 4 and the first hard freeze (28°F) follows near Nov 15. The 32°F date swings from Oct 24 at its earliest to Nov 21 at its latest, near 28 days. The last spring freeze averages Apr 1 and as late as Apr 18, which sets the safe window for reopening outdoor water and de-winterizing gear. At about 14 inches of snow a year, the freeze — not snow load — is the thing to plan around.

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

St. Louis freezes close to Florissant (Nov 13) and later than Belleville (Oct 30) — a reminder that even nearby towns differ by days. Statewide, Missouri prep dates run Oct 19 through Nov 8, which is why St. Louis gets its own number rather than a Missouri-wide average. The same freeze also decides when to winterize an RV and store a motorcycle.

Other winter jobs in St. Louis

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

Sprinklers → Nov 5Frozen pipes → Oct 24Ice dams → Nov 15Car battery → Nov 15Snow blower → Nov 24Sump pump → Apr 1RV → Nov 5Motorcycle → Nov 4

See the full St. Louis 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 15 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 Sci Ctr, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.