FrostList

When to Winterize Your RV in Helena, MT

ON TRACK88 days until first 28°F freezeOct 7

Aim to winterize your RV in Helena by September 27, roughly a week and a half before the median first 28°F freeze of October 7, which one fall in ten shows up by September 25. Plan for the early end: the one-in-ten date lands about 12 days before the median.

OUTLOOK

Typical first first 28°F freeze near Oct 7; local deadline about Sep 27. The live 10-day outlook loads here.

Local freeze dates for Helena

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Sep 17Sep 30Oct 11
28°F (hard freeze)Sep 25Oct 7Oct 22
24°F (severe)Oct 1Oct 18Nov 2

NOAA station: Helena Rgnl AP · 3.8 mi away · 3,828 ft elevation.

For Helena, the nearest NOAA station with freeze data is Helena Rgnl AP, 3.8 miles out at 3,828 feet. Median first-freeze dates there run 32°F by Sep 30, 28°F by Oct 7, 24°F by Oct 18. The 28°F freeze has come as early as Sep 25 and as late as Oct 22, a 27-day spread. Spring's last 32°F freeze clears around May 9. Snowfall averages 37 inches a year, first reaching an inch near October.

Helena usually sees its first 32°F night about Sep 30, with the first 28°F hard freeze close behind near Oct 7. That first freezing night has ranged from Sep 17 to Oct 11, roughly a 24-day spread. On the spring side, the last 32°F freeze clears around May 9 and as late as May 25 — the green light for reopening water and de-winterizing. With around 37 inches of snow annually, plan for a handful of plowable storms each winter.

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

Helena freezes about a week ahead of Great Falls (Oct 11) and later than Bozeman (Oct 3) — a reminder that even nearby towns differ by days. Statewide, Montana prep dates run Sep 23 through Oct 2, which is why Helena gets its own number rather than a Montana-wide average. The same freeze also decides when to shut down your sprinklers and winterize a boat.

Other winter jobs in Helena

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

Sprinklers → Sep 27Frozen pipes → Sep 17Ice dams → Sep 15Car battery → Oct 7Snow blower → Sep 24Sump pump → May 9Boat → Sep 30Motorcycle → Sep 30

See the full Helena 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 Helena?
Wait until the last spring freeze has passed, which averages near May 9 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 Helena Rgnl AP, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.