FrostList

When to Winterize Your RV in Modesto, CA

ON TRACK163 days until first 28°F freezeDec 21

Modesto's median first 28°F hard freeze is December 21 (1991–2020 NOAA normals), and it can strike as early as December 1 — so winterize your RV in Modesto by December 11. It's a short step from frost to a hard freeze: roughly 16 days on average.

OUTLOOK

Typical first first 28°F freeze near Dec 21; local deadline about Dec 11. The live 10-day outlook loads here.

Local freeze dates for Modesto

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Nov 20Dec 5Jan 6
28°F (hard freeze)Dec 1Dec 21Jan 20
24°F (severe)Dec 5Dec 27Jan 15

NOAA station: Modesto City Co AP · 2.7 mi away · 73 ft elevation.

The reference station for Modesto is Modesto City Co AP (2.7 mi, 73 ft). First freeze there: 32°F by Dec 5, 28°F by Dec 21, 24°F by Dec 27. The 28°F freeze has come as early as Dec 1 and as late as Jan 20, a 50-day spread. Spring's last 32°F freeze clears around Jan 31.

Expect the first frost near Dec 5 in Modesto and the first hard freeze by about Dec 21. Year to year, the first 32°F night has fallen anywhere from Nov 20 to Jan 6 — about 47 days apart. Spring's final freeze lands near Jan 31 and as late as Feb 25, so that is when outdoor water and stored gear can safely come back online. Measurable snow is rare, so the freeze near Jan 31 — not snow load — drives the local prep list.

Your rv checklist

  1. Drain the fresh, gray, and black tanks, then drain the water heater only after it has cooled and lost pressure.
  2. Bypass the water heater so you do not waste six gallons of antifreeze filling the tank.
  3. Blow out the lines with a compressor at about 30–40 psi, then pump non-toxic RV antifreeze through every faucet until it runs pink.
    Helpful gear: RV antifreeze (6-pack) — Recommended pick
  4. Use a water-pump converter kit to draw antifreeze straight from the jug through the plumbing.
    Helpful gear: Water pump converter kit — Recommended pick
  5. Pour a cup of antifreeze into each drain trap and the toilet to protect the seals.
  6. Fit a blow-out plug at the city-water inlet so you can clear that line too.
    Helpful gear: Blow-out plug — Recommended pick
  7. Remove batteries or put them on a maintainer, and store them off a cold concrete floor.
  8. Cover roof vents, close the propane, and set out traps or deterrents so mice do not move in.

What to have on hand

RV antifreeze (6-pack)
Non-toxic pink fluid for the fresh-water plumbing and traps.
Recommended pick
Water pump converter kit
Siphon kit that draws antifreeze straight through the pump.
Recommended pick
Blow-out plug
Adapter that lets a compressor clear the lines before antifreeze.
Recommended pick
Heated fresh-water hose
For anyone staying hooked up through a cold snap.
Recommended pick

What this means locally

Modesto freezes close to Ceres (Dec 21) and close to Turlock (Dec 24) — a reminder that even nearby towns differ by days. Statewide, California prep dates run Jan 6 through Dec 27, which is why Modesto gets its own number rather than a California-wide average. The same freeze also decides when to shut down your sprinklers and winterize a boat.

Other winter jobs in Modesto

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

Sprinklers → Dec 11Frozen pipes → Nov 20Car battery → Dec 21Sump pump → Jan 31Boat → Dec 14Motorcycle → Dec 5

See the full Modesto winter checklist, in order →

Frequently asked questions

At what temperature do RV pipes freeze?
An RV's exposed plumbing and thin-walled tanks can begin to freeze once temperatures sit in the mid-20s for a few hours, sooner than a house because there is little insulation around the lines. That is why the winterizing deadline tracks the first 28°F freeze rather than the first light frost.
How much RV antifreeze do I need?
Most travel trailers and motorhomes take about two to three gallons of non-toxic RV antifreeze, and larger rigs more. Bypassing the water heater saves roughly six gallons you would otherwise waste filling the tank. Buy an extra jug; stores sell out once the first freeze warnings hit.
Can I just use my RV furnace instead of winterizing?
Relying on the furnace is risky. A propane run-out, a tripped breaker, or a dead battery during a cold night leaves the plumbing unprotected, and the furnace may not keep the underbelly and bays warm enough anyway. Draining and adding antifreeze is the dependable way to protect the system.
How do I winterize an RV water heater?
Let the tank cool and lose pressure, then drain it and, if fitted, pull the anode rod. Do not add antifreeze to the water heater tank; instead, set the bypass valves so antifreeze skips the tank and fills only the lines. Fresh antifreeze in an unbypassed heater just wastes several gallons.
When is it safe to de-winterize an RV in Modesto?
Wait until the last spring freeze has passed, which averages near Jan 31 here. De-winterize by flushing the antifreeze from the lines, sanitizing the fresh tank, and checking for leaks before a trip. Reopening too early risks a surprise late freeze on a charged system.
Do I need to winterize an RV stored indoors?
A reliably heated indoor space that stays above freezing protects the plumbing, so full winterizing may not be needed. But an unheated garage or barn can still drop below freezing on a cold night. If you cannot guarantee the space stays warm, winterize to be safe.

Data: NOAA 1991–2020 normals via Modesto City Co AP, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.