FrostList

When to Test Your Sump Pump in South San Francisco, CA

ON TRACK171 days until spring thaw test (last 32°F)Dec 29

In South San Francisco the spring thaw peaks around the last 32°F freeze, near December 29 (1991–2020 normals) — a good twice-a-year cue, with the fall rains, to pour five gallons in the pit and watch the pump run.

OUTLOOK

Typical first spring thaw test (last 32°F) near Dec 29; local deadline about Dec 29. The live 10-day outlook loads here.

Local freeze dates for South San Francisco

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

NOAA station: San Francisco Intl AP · 3.4 mi away · 8 ft elevation.

Numbers for South San Francisco come from San Francisco Intl AP, 3.4 miles away at 8 feet, where the medians fall 32°F by Dec 26. Spring's last 32°F freeze clears around Dec 29.

In South San Francisco, the first freezing night (32°F) typically arrives around Dec 26; a full 28°F hard freeze is uncommon here. That first freezing night has ranged from Dec 11 to Jan 13, roughly a 33-day spread. On the spring side, the last 32°F freeze clears around Dec 29 and as late as Jan 13 — the green light for reopening water and de-winterizing. With almost no snow in a normal year, cold — not plowing — sets the calendar, and it centers on Dec 29.

Your sump pump checklist

  1. Pour about five gallons of water into the pit slowly and watch the float rise, the pump start, and the water drop.
    Helpful gear: Water level alarm — Recommended pick
  2. Confirm the discharge line carries water 10–20 feet from the foundation and does not drain back into the pit.
    Helpful gear: Sump check valve — Recommended pick
  3. Clear the inlet screen and the pit of gravel and debris that can jam the float or the impeller.
  4. Check the check valve for a firm click; a failed valve lets discharged water fall back and short-cycle the pump.
  5. Add a battery backup pump so the system still runs when a storm knocks out the power.
    Helpful gear: Battery backup sump pump — Recommended pick
  6. Test the backup on battery power and note the install date; batteries usually need replacing every few years.
  7. If the primary pump is 7–10 years old, keep a replacement on the shelf before it fails mid-storm.
    Helpful gear: Replacement primary pump — Recommended pick
  8. Remember that flood insurance and most homeowner policies treat pump failure separately — read your coverage.

What to have on hand

Battery backup sump pump
Second pump that runs when the power goes out mid-storm.
Recommended pick
Water level alarm
Loud sensor that warns you before the pit overflows.
Recommended pick
Sump check valve
One-way valve that stops discharged water from draining back.
Recommended pick
Replacement primary pump
A ready spare for a pump nearing the end of its life.
Recommended pick

What this means locally

South San Francisco freezes close to San Bruno (Dec 29) and close to Daly City (Dec 30) — a reminder that even nearby towns differ by days. Statewide, California prep dates run Jan 1 through Dec 31, which is why South San Francisco gets its own number rather than a California-wide average. The same freeze also decides when to protect your pipes.

Other winter jobs in South San Francisco

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

Frozen pipes → Dec 11Motorcycle → Dec 26

See the full South San Francisco winter checklist, in order →

Frequently asked questions

How do I test my sump pump before heavy rain?
Pour about five gallons of water into the pit slowly and watch the float rise, the pump switch on, and the water level drop. Confirm the discharge carries water well away from the foundation. Doing this before the wet season, and again in spring near the last freeze around Dec 29, catches problems early.
How often should a sump pump run?
It varies with your water table and weather; some pumps cycle every few minutes during a storm and sit idle for weeks in dry spells. Frequent cycling with no rain can signal a stuck float, a failed check valve, or groundwater seeping in. Occasional running during wet weather is normal.
How long do sump pumps last?
A typical sump pump lasts about 7 to 10 years, though hard-working pumps wear out sooner. If yours is near that age, keep a replacement on hand so a mid-storm failure does not leave the pit unattended. Testing it seasonally tells you more than age alone.
Do I need a battery backup sump pump?
If your basement floods when the power goes out, yes — storms that overwhelm the pit are exactly when the grid tends to fail. A battery backup runs the pump through an outage, which is the single most common cause of a wet basement during heavy weather. Test the backup on battery power, too.
Does insurance cover sump pump failure?
Standard homeowner policies and federal flood insurance often exclude damage from a sump pump that fails or is overwhelmed. A separate water-backup or sump-failure rider may be available. Read your policy before a storm, because assumptions about coverage are a common and costly surprise.
Why is my sump pump running with no rain?
A high water table, snowmelt, or groundwater seepage can keep the pit filling even in dry weather. A pump that runs constantly may also have a stuck float switch or a check valve that lets discharged water fall back into the pit. Check the float and the valve first.

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