FrostList

When to Prevent Frozen Pipes in San Mateo, CA

ON TRACK168 days until first freezing night (32°F)Dec 26

In San Mateo, plan for freezing nights from about December 26 onward — one year in ten by December 11 — and treat any low in the low 20s as a pipe-risk night.

OUTLOOK

Typical first first freezing night (32°F) near Dec 26; local deadline about Dec 11. The live 10-day outlook loads here.

Local freeze dates for San Mateo

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Dec 11Dec 26Jan 13

NOAA station: San Francisco Intl AP · 4.5 mi away · 8 ft elevation.

The reference station for San Mateo is San Francisco Intl AP (4.5 mi, 8 ft). First freeze there: 32°F by Dec 26. Spring's last 32°F freeze clears around Dec 29.

The first frost in San Mateo lands near Dec 26, and temperatures seldom push down to a hard 28°F. The 32°F date swings from Dec 11 at its earliest to Jan 13 at its latest, near 33 days. The last spring freeze averages Dec 29 and as late as Jan 13, which sets the safe window for reopening outdoor water and de-winterizing gear. Snow barely registers here; the freeze date, around Dec 29, 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, San Mateo (first freeze Dec 26) runs close to San Bruno (Dec 26) and later than Redwood City (Dec 12). Across California, local prep deadlines in our data range from Oct 17 to Dec 23, so a statewide rule of thumb would miss San Mateo by weeks.

Other winter jobs in San Mateo

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

Sump pump → Dec 29Motorcycle → Dec 26

See the full San Mateo 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 San Mateo?
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 26.
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 San Francisco Intl AP, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.