FrostList

When to Winterize Your RV in Union City, CA

ON TRACK171 days until first 28°F freezeDec 29

Aim to winterize your RV in Union City by December 19, roughly a week and a half before the median first 28°F freeze of December 29, which one fall in ten shows up by December 11. Year to year the date swings about 37 days, which is why the live outlook beats the calendar.

OUTLOOK

Typical first first 28°F freeze near Dec 29; local deadline about Dec 19. The live 10-day outlook loads here.

Local freeze dates for Union City

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Dec 2Dec 22Jan 21
28°F (hard freeze)Dec 11Dec 29Jan 17

NOAA station: Fremont · 3.9 mi away · 38 ft elevation.

The reference station for Union City is Fremont (3.9 mi, 38 ft). First freeze there: 32°F by Dec 22, 28°F by Dec 29. The 28°F freeze has come as early as Dec 11 and as late as Jan 17, a 37-day spread. Spring's last 32°F freeze clears around Jan 7.

In Union City, freezing nights (32°F) typically begin around Dec 22 and the first hard freeze (28°F) follows near Dec 29. Year to year, the first 32°F night has fallen anywhere from Dec 2 to Jan 21 — about 50 days apart. Spring's final freeze lands near Jan 7 and as late as Feb 7, so that is when outdoor water and stored gear can safely come back online. Measurable snow is rare, so the freeze near Jan 7 — 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

Union City freezes close to Fremont (Dec 29) and later than Dublin (Dec 18) — a reminder that even nearby towns differ by days. Statewide, California prep dates run Jan 6 through Dec 27, which is why Union City 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 Union City

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

Sprinklers → Dec 19Frozen pipes → Dec 2Car battery → Dec 29Sump pump → Jan 7Boat → Dec 22Motorcycle → Dec 22

See the full Union City 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 Union City?
Wait until the last spring freeze has passed, which averages near Jan 7 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 Fremont, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.