Will Pipes Freeze in San Francisco County, CA? No Normal Risk Nights
Freeze nights in San Francisco County
A normal winter in San Francisco County, CA never drops to 20°F, the point where bare pipes in unheated space start to freeze.
Risk level: No normal risk nights.
It depends where the pipe is
| Pipe | Freezes near | Nights a year |
|---|---|---|
| Outdoor spigot, open crawlspace | 32°F | 3 nights |
| Bare pipe in garage, attic or outside wall | 20°F | none |
| Insulated pipe in unheated space | 10°F | none |
| Inside the heated house | 0°F | none |
Month by month
Nights at or below 20°F in a normal year.
First 32°F night is usually around 12/25, last around 12/30.
How cold San Francisco County nights get
Average winter (Dec-Feb) low: 44°F; the coldest month, December, averages 44°F overnight. 2 months normally bring at least one night below 32°F (Jan, Dec).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 44°F | 45°F | 46°F | 48°F | 50°F | 53°F | 54°F | 55°F | 54°F | 52°F | 47°F | 44°F |
San Francisco County next to its neighbours
The six closest counties all sit within a night of San Francisco County.
| County | Distance | Below 32°F | Below 20°F | Jan low |
|---|---|---|---|---|
| San Francisco County, CA | - | 3 nights | none | 44°F |
| Marin County, CA | 44 km northeast | 7 nights | none | 42°F |
| San Mateo County, CA | 68 km southeast | 18 nights | none | 40°F |
| Sonoma County, CA | 89 km north | 18 nights | under 1 night | 40°F |
| Contra Costa County, CA | 97 km east | 11 nights | none | 42°F |
| Alameda County, CA | 99 km east | 14 nights | none | 39°F |
| Napa County, CA | 106 km northeast | 17 nights | none | 39°F |
San Francisco County within CA
San Francisco County ranks 56 of 58 CA counties for nights below 20°F. The most is Mono County, CA at 130 nights, with a 13°F average winter low. The fewest is Orange County, CA: none, winter lows near 46°F. At -45 ft, San Francisco County sits 1,344 ft below the state's median county elevation of 1,298 ft.
What to do here
- Disconnect hoses in a cold snap; no routine prep needed.
Even here, a once-a-decade freeze catches houses built without insulation: why pipes burst in warm places.
Where this comes from
NOAA 1991-2020 climate normals, blended from 3 nearby stations and adjusted for elevation; closest is San Francisco Oceanside, CA, 46 km away (fair match). A normal year, not tonight's forecast: check the forecast low for the night itself. Why elevation is part of the blend: how county numbers are made.