Weather in South San Francisco, California
Fog and sun in daily rhythm. Day 59 of spring. Read this microseason across nine climate regions →
- TodayMay 16Mostly Clear—66°53°
- SundayMay 17Overcast—74°50°
- MondayMay 18Clear—74°57°
- TuesdayMay 19Mostly Clear—81°54°
- WednesdayMay 20Overcast—75°54°
- ThursdayMay 21Overcast—75°54°
- FridayMay 22Overcast—71°55°
- PM 2.5
- 8.9 μg/m³
- PM 10
- 14.5 μg/m³
- NO₂
- 2.0 μg/m³
- Ozone
- 84.0 μg/m³
- UV Index
- 2.3 Low
When the dew is on the grass, rain will never come to pass.
- Moonrise
- 1:12 PM
- Moonset
- 3:47 AM
- In sign
- ♉︎ Taurus
Fog and sun in daily rhythm
South San Francisco at a glance
- Today vs. normal: 12°F below the seasonal normal for this latitude
- Last frost: April 2 (climatological average for this latitude)
- Microseason: 28 of 72, May 16–20
- Planting window: Direct sow okra, melons, and southern peas. Thin carrot rows.
Right now in the garden
Warm-season window is open
As of May 17, the last spring frost has passed for most years. Transplant tomatoes, peppers, eggplants, basil, and cucurbits (cucumbers, squash, melons) now. Direct-sow beans and corn into warm soil.
Planting calendar
| Month | Plant | Harvest |
|---|---|---|
| January | — | — |
| February | — | — |
| March | — | — |
| April | lettuce, peas, spinach, radishes | — |
| May | lettuce, peas, spinach, radishes, tomatoes, peppers, beans, squash | lettuce, peas, radishes |
| June | tomatoes, peppers, beans, squash | lettuce, peas, radishes |
| July | tomatoes, peppers, beans, squash | tomatoes, beans, summer squash |
| August | — | tomatoes, beans, summer squash |
| September | fall brassicas, garlic (overwinter), carrots | tomatoes, beans, summer squash |
| October | fall brassicas, garlic (overwinter), carrots | winter squash, tomatoes (last) |
| November | — | — |
| December | — | — |
A year in weather
South San Francisco's warmest month is September (~63°F mean) and its coldest is January (~52°F). Rainfall peaks in December (4.8 inches) and bottoms out in July (0.0 inches).
| Month | Mean temp | Precip | Rainy days |
|---|---|---|---|
| January | 52° | 4.4″ | 8 |
| February | 54° | 4.4″ | 8 |
| March | 56° | 3.1″ | 7 |
| April | 56° | 1.6″ | 4 |
| May | 58° | 0.7″ | 2 |
| June | 60° | 0.2″ | 1 |
| July | 60° | 0.0″ | 0 |
| August | 62° | 0.1″ | 0 |
| September | 63° | 0.1″ | 0 |
| October | 62° | 0.9″ | 2 |
| November | 57° | 2.6″ | 5 |
| December | 53° | 4.8″ | 8 |
Regional context
South San Francisco sits within a hot-summer Mediterranean climate region — a cohort that shares similar temperature ranges, seasonal patterns, and growing conditions across nearby cities.
Similar climates: Los Angeles, CA, San Francisco, CA, San Diego, CA, Riverside, CA, Sacramento, CA.
Frequently asked
- When does it freeze in South San Francisco?
- South San Francisco's last spring frost typically falls around mid-April, and the first fall frost arrives around mid-November.
- What is the rainy season in South San Francisco?
- December is the wettest month with about 4.8 inches of rain on average; the city receives roughly 23 inches annually.
- What is the warmest month in South San Francisco?
- September is typically warmest, averaging about 63°F.
- What is the coldest month in South San Francisco?
- January is typically coldest, averaging about 52°F.
- When can I start a vegetable garden in South San Francisco?
- Cool-season crops (peas, lettuce) can be sown around the last spring frost (mid-April); warm-season crops (tomatoes, peppers) wait until 1–2 weeks after.
- How many rainy days does South San Francisco get?
- South San Francisco averages about 45 rainy days per year.
- What hardiness zone is South San Francisco?
- South San Francisco's USDA hardiness zone is determined by its lowest average winter temperature; check the USDA's online lookup with the city ZIP for the current zone designation.
Climate
South San Francisco, California sits in a hot-summer Mediterranean climate zone. January means hover near 52°F while July averages 60°F — a 8°F seasonal swing.
Across the year, South San Francisco receives about 23 inches of precipitation spread over roughly 45 rainy days.
The rhythm of the year is set by latitude (37.7°N), proximity to large water bodies, and elevation — all of which shape what grows here, when frost is likely, and what the weather story looks like day to day.