USDA Hardiness Zone 10a
Frost Dates for 94401 — San Mateo, California
NOAA 1991–2020 normals from San Francisco International Airport, CA (8 ft), 4 miles northwest.
Updated
Frost is not a yearly event in San Mateo: a night at or below 32°F came in 12% of the winters of 1991–2020 at San Francisco International Airport, CA, and a 36°F night, cold enough for frost on exposed leaves, in 70%. There is no reliable "last frost date" here; most years have none.
- Winters with a freeze
- 12%
- Winters with 36°F
- 70%
- Coldest month low
- 45°F
- Hardiness zone
- 10a
32°F or below, 1991–2020
frost possible on leaves
average, January
30 to 35°F (-1.1 to 1.7°C) coldest night
- First snow
- Rare
- Last snow
- Rare
- Winters with snow
- 5%
- Snow per year
- 0"
median, 1991–2020
median, 1991–2020
1 of 19 observed
NOAA normal
Frost risk by date in San Mateo
At San Francisco International Airport, CA, 4 miles northwest of San Mateo, 12% of the winters of 1991–2020 had at least one night at or below 32°F, and none reached 28°F. Nights of 36°F, enough for frost on exposed leaves, are more common (70% of winters) and, when they come, fall between about December 24 and January 8. December is the month most likely to bring one: a 8% chance in a given year. 62 of the 283 other California stations behind this site's ZIP pages freeze in fewer than half of winters too.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F70% of yrs | Dec 16 | Dec 25 | Dec 30 | Jan 3 | Jan 8 | Jan 15 | Jan 22 | Jan 30 | Feb 14 |
| 32°F12% of yrs | too rare for a date | ||||||||
| 28°F0% of yrs | never in 1991–2020 | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F70% of yrs | Dec 5 | Dec 10 | Dec 15 | Dec 19 | Dec 24 | Dec 28 | Jan 1 | Jan 9 | Jan 24 |
| 32°F12% of yrs | too rare for a date | ||||||||
| 28°F0% of yrs | never in 1991–2020 | ||||||||
Freeze probabilities 1991–2020 at San Francisco International Airport, CA, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 94401 →Compare San Mateo with another place →
Weather by month in San Mateo
September is the warmest month at San Francisco International Airport, CA, averaging 75°F by day and 56°F at night; January is the coldest at 58°F and 45°F. Every month stays under a 10% chance of a 32°F night; December is the likeliest at 8%.
Warmth for growing adds up to 3,281 growing degree days a year (base 50°F), fewer than at 77% of the 283 California stations. 38% of them (1,258) have built up by the end of June, and August adds the most, 462. Precipitation totals 19.6 inches a year, most in December (4.1") and least in July (0.0"); May to September bring 4% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 58 | 45 | 3.9 | 4% | 0 | 69 |
| Feb | 61 | 46 | 4.0 | 0% | 0 | 108 |
| Mar | 63 | 48 | 2.7 | 0% | 0 | 174 |
| Apr | 66 | 49 | 1.4 | 0% | 0 | 221 |
| May | 68 | 52 | 0.5 | 0% | 0 | 309 |
| Jun | 72 | 54 | 0.1 | 0% | 0 | 377 |
| Jul | 73 | 55 | 0.0 | 0% | 0 | 432 |
| Aug | 73 | 56 | 0.0 | 0% | 0 | 462 |
| Sep | 75 | 56 | 0.1 | 0% | 0 | 461 |
| Oct | 72 | 53 | 0.8 | 0% | 0 | 398 |
| Nov | 64 | 49 | 2.0 | 0% | 0 | 196 |
| Dec | 58 | 45 | 4.1 | 8% | <1 | 74 |
Monthly normals 1991–2020 at San Francisco International Airport, CA (8 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, Redwood City, CA, 8 miles southeast of San Mateo, has a 32°F night in 88% of winters against 12% here, and a coolest-month low 5°F colder (40°F).
When it snows in San Mateo, California
Measurable snow is rare here: only 1 of 19 winters from 1991 to 2020 recorded 0.1 inch or more at Redwood City, CA, 7.9 miles away, so there is no typical first-snow date to plan around.
Where these figures come from
ZIP 94401 is 4 miles from San Francisco International Airport, CA, which stands at 8 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 6 other ZIP codes share the station; its figures are presented in full for 94080 (South San Francisco). The 2023 USDA Plant Hardiness Zone Map lists ZIP 94401 in zone 10a, the band where the coldest night of the year averaged 30 to 35°F (-1.1 to 1.7°C) over 1991–2020; a zone describes winter lows, not frost dates.
Frost dates across California →
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.