FrostList

When to Winterize Your Boat in Commerce City, CO

ON TRACK99 days until first 28°F freezeOct 18

The first 28°F freeze near Commerce City averages October 18 (1991–2020 normals) — enough to crack an unprotected block even where owners assume they're safe — so winterize the boat by October 11. 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 Oct 18; local deadline about Oct 11. The live 10-day outlook loads here.

Local freeze dates for Commerce City

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Sep 25Oct 8Oct 20
28°F (hard freeze)Oct 3Oct 18Oct 31
24°F (severe)Oct 12Oct 27Nov 12

NOAA station: Denver-Stapleton · 4.6 mi away · 5,286 ft elevation.

The reference station for Commerce City is Denver-Stapleton (4.6 mi, 5,286 ft). First freeze there: 32°F by Oct 8, 28°F by Oct 18, 24°F by Oct 27. That hard freeze has landed anywhere from Oct 3 to Oct 31, a swing of roughly 28 days. Spring's last 32°F freeze clears around May 4. Snowfall averages 49 inches a year, first reaching an inch near October.

Commerce City usually sees its first 32°F night about Oct 8, with the first 28°F hard freeze close behind near Oct 18. That first freezing night has ranged from Sep 25 to Oct 20, roughly a 25-day spread. On the spring side, the last 32°F freeze clears around May 4 and as late as May 16 — the green light for reopening water and de-winterizing. Snow totals near 49 inches a year mean plowing and ice-dam control share the winter to-do list here.

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

Against its neighbors, Commerce City (first freeze Oct 18) runs close to Thornton (Oct 21) and close to Denver (Oct 21). Across Colorado, local prep deadlines in our data range from Oct 3 to Oct 26, so a statewide rule of thumb would miss Commerce City by weeks. In Commerce City, that same cold is your cue to winterize an RV and store a motorcycle.

Other winter jobs in Commerce City

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

Sprinklers → Oct 8Frozen pipes → Sep 25Ice dams → Sep 15Car battery → Oct 18Snow blower → Sep 24Sump pump → May 4RV → Oct 8Motorcycle → Oct 8

See the full Commerce City 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 Oct 18 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 CO 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 Denver-Stapleton, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.