FrostList

When to Prevent Frozen Pipes in Sunnyvale, CA

ON TRACK165 days until first freezing night (32°F)Dec 23

In Sunnyvale, plan for freezing nights from about December 23 onward — one year in ten by December 3 — and treat any low in the low 20s as a pipe-risk night. The early-odds date runs roughly 18 days ahead of the median, so build in that buffer.

OUTLOOK

Typical first first freezing night (32°F) near Dec 23; local deadline about Dec 3. The live 10-day outlook loads here.

Local freeze dates for Sunnyvale

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Dec 3Dec 23Jan 16
28°F (hard freeze)Dec 13Dec 31Jan 22

NOAA station: Moffett Federal Airfield · 2.6 mi away · 39 ft elevation.

For Sunnyvale, the nearest NOAA station with freeze data is Moffett Federal Airfield, 2.6 miles out at 39 feet. Median first-freeze dates there run 32°F by Dec 23, 28°F by Dec 31. That hard freeze has landed anywhere from Dec 13 to Jan 22, a swing of roughly 40 days. Spring's last 32°F freeze clears around Jan 6.

The freeze arrives in two steps in Sunnyvale: 32°F around Dec 23, then a hard 28°F near Dec 31. The 32°F date swings from Dec 3 at its earliest to Jan 16 at its latest, near 44 days. The last spring freeze averages Jan 6 and as late as Feb 4, which sets the safe window for reopening outdoor water and de-winterizing gear. Snow barely registers here; the freeze date, around Jan 6, is the one that matters.

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

Against its neighbors, Sunnyvale (first freeze Dec 23) runs close to Mountain View (Dec 23) and close to Cupertino (Dec 23). Across California, local prep deadlines in our data range from Oct 17 to Dec 23, so a statewide rule of thumb would miss Sunnyvale by weeks. In Sunnyvale, that same cold is your cue to shut down your sprinklers and check your car battery.

Other winter jobs in Sunnyvale

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

Sprinklers → Dec 21Car battery → Dec 31Sump pump → Jan 6RV → Dec 21Boat → Dec 24Motorcycle → Dec 23

See the full Sunnyvale 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 Sunnyvale?
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 23.
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 Moffett Federal Airfield, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.