FrostList

When to Winterize Your Boat in Tempe, AZ

ON TRACK161 days until first 28°F freezeDec 19

In Tempe, target December 12 to drain, antifreeze, and lay up the boat, about a week before the median first 28°F freeze of December 19; a surprise cold snap is exactly how freeze claims happen. 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 19; local deadline about Dec 12. The live 10-day outlook loads here.

Local freeze dates for Tempe

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Nov 18Dec 5Dec 24
28°F (hard freeze)Nov 27Dec 19Jan 19
24°F (severe)Dec 4Dec 31Jan 24

NOAA station: Tempe Asu · 1.1 mi away · 1,167 ft elevation.

The reference station for Tempe is Tempe Asu (1.1 mi, 1,167 ft). First freeze there: 32°F by Dec 5, 28°F by Dec 19, 24°F by Dec 31. That hard freeze has landed anywhere from Nov 27 to Jan 19, a swing of roughly 53 days. Spring's last 32°F freeze clears around Feb 13.

Expect the first frost near Dec 5 in Tempe and the first hard freeze by about Dec 19. The 32°F date swings from Nov 18 at its earliest to Dec 24 at its latest, near 36 days. The last spring freeze averages Feb 13 and as late as Mar 9, which sets the safe window for reopening outdoor water and de-winterizing gear. Snow barely registers here; the freeze date, around Feb 13, 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, Tempe's first-freeze date near Dec 19 sits close to Scottsdale (Dec 19) and close to Mesa (Dec 19). Arizona's deadlines span Oct 2 to Dec 28 statewide — one date for all of Arizona would be off by weeks for Tempe. Once you know Tempe's freeze date, use it to winterize an RV and store a motorcycle too.

Other winter jobs in Tempe

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

Sprinklers → Dec 9Frozen pipes → Nov 18Car battery → Dec 19Sump pump → Feb 13RV → Dec 9Motorcycle → Dec 5

See the full Tempe 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 19 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 AZ 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 Tempe Asu, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.