FrostList

When to Winterize Your RV in San Bernardino, CA

SEASON PASSED174 days until first 28°F freezeJan 1

San Bernardino's median first 28°F hard freeze is January 1 (1991–2020 NOAA normals), and it can strike as early as December 13 — so winterize your RV in San Bernardino by December 22. The early-odds date runs roughly 19 days ahead of the median, so build in that buffer.

OUTLOOK

Typical first first 28°F freeze near Jan 1; local deadline about Dec 22. The live 10-day outlook loads here.

Local freeze dates for San Bernardino

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Dec 1Dec 19Jan 26
28°F (hard freeze)Dec 13Jan 1Feb 13

NOAA station: Redlands · 7.3 mi away · 1,410 ft elevation.

The reference station for San Bernardino is Redlands (7.3 mi, 1,410 ft). First freeze there: 32°F by Dec 19, 28°F by Jan 1. Year to year the 28°F date has ranged from Dec 13 to Feb 13 — about 62 days apart. Spring's last 32°F freeze clears around Jan 27.

In San Bernardino, freezing nights (32°F) typically begin around Dec 19 and the first hard freeze (28°F) follows near Jan 1. The 32°F date swings from Dec 1 at its earliest to Jan 26 at its latest, near 56 days. The last spring freeze averages Jan 27 and as late as Feb 28, which sets the safe window for reopening outdoor water and de-winterizing gear. Snow barely registers here; the freeze date, around Jan 27, is the one that matters.

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

Against its neighbors, San Bernardino (first freeze Jan 1) runs close to Colton (Jan 1) and close to Highland (Jan 1). Across California, local prep deadlines in our data range from Jan 6 to Dec 27, so a statewide rule of thumb would miss San Bernardino by weeks. In San Bernardino, that same cold is your cue to shut down your sprinklers and winterize a boat.

Other winter jobs in San Bernardino

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

Sprinklers → Dec 22Frozen pipes → Dec 1Car battery → Jan 1Sump pump → Jan 27Boat → Dec 25Motorcycle → Dec 19

See the full San Bernardino 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 San Bernardino?
Wait until the last spring freeze has passed, which averages near Jan 27 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 Redlands, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.