FrostList

When to Prevent Frozen Pipes in Union City, CA

ON TRACK164 days until first freezing night (32°F)Dec 22

In Union City, plan for freezing nights from about December 22 onward — one year in ten by December 2 — and treat any low in the low 20s as a pipe-risk night. Year to year the date swings about 37 days, which is why the live outlook beats the calendar.

OUTLOOK

Typical first first freezing night (32°F) near Dec 22; local deadline about Dec 2. 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 frozen pipes checklist

  1. Disconnect, drain, and store garden hoses, then shut off and drain any interior valves that feed outdoor faucets.
  2. Insulate exposed pipes in the garage, crawl space, and along exterior walls with foam sleeves rated for the pipe size.
    Helpful gear: Foam pipe insulation sleeves — Recommended pick
  3. On nights in the low 20s, let a pencil-thin stream of water drip from the faucet farthest from where the line enters.
  4. Open cabinet doors under kitchen and bathroom sinks on outside walls so household heat reaches the plumbing.
  5. Add self-regulating heat cable to the runs most likely to freeze, such as a pipe in an unheated garage.
    Helpful gear: Self-regulating heat cable — Recommended pick
  6. Cap outdoor faucets with insulated covers once the hoses are off.
    Helpful gear: Outdoor faucet covers — Recommended pick
  7. Know where your main shutoff is and confirm it turns; a fast shutoff limits water damage if a line lets go.
  8. If you travel, keep the thermostat at 55°F or higher and ask someone to check the house during a cold snap.
    Helpful gear: Wi-Fi water leak sensor — Recommended pick

What to have on hand

Foam pipe insulation sleeves
Split foam tubing for exposed pipes in crawl spaces and garages.
Recommended pick
Self-regulating heat cable
Thermostatic cable that warms vulnerable runs only when it is cold.
Recommended pick
Outdoor faucet covers
Insulated caps for hose bibs once the hoses come off.
Recommended pick
Wi-Fi water leak sensor
Puck that pings your phone the moment it senses water.
Recommended pick

What this means locally

Union City freezes close to Fremont (Dec 22) and about a week ahead of Newark (Dec 27) — a reminder that even nearby towns differ by days. Statewide, California prep dates run Oct 17 through Dec 23, 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 check your car battery.

Other winter jobs in Union City

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

Sprinklers → Dec 19Car battery → Dec 29Sump pump → Jan 7RV → Dec 19Boat → Dec 22Motorcycle → Dec 22

See the full Union City winter checklist, in order →

Frequently asked questions

At what temperature do pipes freeze?
Pipes generally come under risk when the temperature outside falls to about 20°F, the threshold many guides use for taking action. Pipes in unheated or exterior-wall spaces freeze sooner than well-insulated interior runs. Wind and poor insulation lower the effective temperature, so a windy night in the mid-20s can be as risky as a still night in the low 20s.
Should I drip my faucets tonight in Union City?
If the overnight low is forecast at or below about 20°F, letting a thin stream run from the faucet farthest along the line is a low-cost precaution. Moving water is slower to freeze and relieves pressure. Check tonight's low against the live outlook above; freezing nights here typically begin around Dec 22.
How long does it take for pipes to freeze?
There is no fixed clock; it depends on pipe location, insulation, and how far below freezing the air drops. An exposed pipe in a windy, unheated space can freeze in a matter of hours during a hard cold snap, while a protected interior pipe may never reach freezing. The colder and windier it is, the faster it happens.
Which pipes freeze first?
The most exposed pipes freeze first: outdoor hose bibs, and lines in unheated garages, crawl spaces, attics, and along exterior walls. Pipes under sinks on outside walls are common trouble spots. That is why disconnecting hoses and opening cabinet doors on cold nights are two of the highest-value steps.
Does homeowners insurance cover burst pipes?
Sudden, accidental water damage from a frozen pipe is often covered, but insurers may deny a claim if the home was left unheated or the damage is judged to be from neglect. Coverage varies by policy. Keeping the heat on and taking reasonable precautions helps protect both your home and your claim.
What temperature should I keep my house if I'm away?
A common recommendation is to keep the thermostat no lower than 55°F while you are away so interior walls stay warm enough to protect the plumbing. Leaving cabinet doors open and having someone check the house during a cold snap adds a margin of safety, especially for pipes on exterior walls.

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