FrostList

When to Winterize Your Boat in Casper, WY

ON TRACK87 days until first 28°F freezeOct 6

The first 28°F freeze near Casper averages October 6 (1991–2020 normals) — enough to crack an unprotected block even where owners assume they're safe — so winterize the boat by September 29. The early-to-late range spans roughly 32 days, so treat the median as a midpoint, not a promise.

OUTLOOK

Typical first first 28°F freeze near Oct 6; local deadline about Sep 29. The live 10-day outlook loads here.

Local freeze dates for Casper

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Sep 14Sep 29Oct 12
28°F (hard freeze)Sep 21Oct 6Oct 23
24°F (severe)Sep 30Oct 17Nov 1

NOAA station: Casper Wwtp · 1.1 mi away · 5,097 ft elevation.

The reference station for Casper is Casper Wwtp (1.1 mi, 5,097 ft). First freeze there: 32°F by Sep 29, 28°F by Oct 6, 24°F by Oct 17. Year to year the 28°F date has ranged from Sep 21 to Oct 23 — about 32 days apart. Spring's last 32°F freeze clears around May 10. Snowfall averages 72 inches a year, first reaching an inch near September.

Expect the first frost near Sep 29 in Casper and the first hard freeze by about Oct 6. Year to year, the first 32°F night has fallen anywhere from Sep 14 to Oct 12 — about 28 days apart. Spring's final freeze lands near May 10 and as late as May 24, so that is when outdoor water and stored gear can safely come back online. With about 72 inches of snow a year, roof, snow-blower, and ice-dam prep all belong on the same calendar.

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, Casper (first freeze Oct 6) runs about a week ahead of Cheyenne (Oct 10) and about a week ahead of Fort Collins (Oct 17). Across Wyoming, local prep deadlines in our data range from Sep 29 to Oct 3, so a statewide rule of thumb would miss Casper by weeks. In Casper, that same cold is your cue to winterize an RV and store a motorcycle.

Other winter jobs in Casper

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

Sprinklers → Sep 26Frozen pipes → Sep 14Ice dams → Aug 16Car battery → Oct 6Snow blower → Aug 25Sump pump → May 10RV → Sep 26Motorcycle → Sep 29

See the full Casper 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 6 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 WY 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 Casper Wwtp, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.