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Foster City, California climate
Csb Warm-summer Mediterranean
Foster City has a mildly seasonal mild-temperate climate (Warm-summer Mediterranean, Köppen Csb). The hottest month is July with an average daily high near 27°C, while the coldest is December averaging around 5°C at night. Precipitation totals about 483 mm a year and is strongly seasonal — December alone averages 100 mm while July barely receives 0 mm.
Temperature & precipitation
Daily high–low temperature range with the monthly average, plus monthly precipitation · 1991–2020 normals · hover a month for the exact figuresClear vs cloudy days
Share of days each month that are clear, partly cloudy or cloudy · 1991–2020 · hover a month for the day countsFoster City climate normals (1991–2020)
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high (°C) | 15 | 17 | 19 | 20 | 23 | 26 | 27 | 27 | 26 | 24 | 18 | 15 |
| Avg temp (°C) | 10 | 11 | 13 | 14 | 16 | 19 | 20 | 20 | 19 | 17 | 12 | 10 |
| Avg low (°C) | 5 | 6 | 7 | 8 | 10 | 12 | 14 | 14 | 12 | 10 | 7 | 5 |
| Precipitation (mm) | 97 | 93 | 77 | 29 | 12 | 4 | 0 | 1 | 2 | 22 | 47 | 100 |
| Jan – Jun | Jan | Feb | Mar | Apr | May | Jun |
|---|---|---|---|---|---|---|
| Avg high (°C) | 15 | 17 | 19 | 20 | 23 | 26 |
| Avg temp (°C) | 10 | 11 | 13 | 14 | 16 | 19 |
| Avg low (°C) | 5 | 6 | 7 | 8 | 10 | 12 |
| Precipitation (mm) | 97 | 93 | 77 | 29 | 12 | 4 |
| Jul – Dec | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|
| Avg high (°C) | 27 | 27 | 26 | 24 | 18 | 15 |
| Avg temp (°C) | 20 | 20 | 19 | 17 | 12 | 10 |
| Avg low (°C) | 14 | 14 | 12 | 10 | 7 | 5 |
| Precipitation (mm) | 0 | 1 | 2 | 22 | 47 | 100 |
How often — frequency of weather events
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Days with measurable rain (days) | 8 | 8 | 9 | 5 | 3 | 0.9 | 0.0 | 0.2 | 0.5 | 2 | 6 | 9 |
| Days with high ≥ 32°C (days) | — | — | — | 0.3 | 1 | 4 | 3 | 3 | 4 | 1 | — | — |
| Days with low ≤ 0°C (days) | 2 | 0.6 | — | — | — | — | — | — | 0.0 | — | 0.4 | 2 |
| Jan – Jun | Jan | Feb | Mar | Apr | May | Jun |
|---|---|---|---|---|---|---|
| Days with measurable rain (days) | 8 | 8 | 9 | 5 | 3 | 0.9 |
| Days with high ≥ 32°C (days) | — | — | — | 0.3 | 1 | 4 |
| Days with low ≤ 0°C (days) | 2 | 0.6 | — | — | — | — |
| Jul – Dec | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|
| Days with measurable rain (days) | 0.0 | 0.2 | 0.5 | 2 | 6 | 9 |
| Days with high ≥ 32°C (days) | 3 | 3 | 4 | 1 | — | — |
| Days with low ≤ 0°C (days) | — | — | 0.0 | — | 0.4 | 2 |
Sky & atmosphere
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Cloud cover (%) | 60 | 61 | 60 | 55 | 54 | 48 | 58 | 59 | 51 | 47 | 51 | 57 |
| Clear days (≤ 30% cloud) | 7 | 6 | 7 | 8 | 8 | 10 | 4 | 4 | 9 | 11 | 10 | 8 |
| Partly cloudy days (30–70%) | 9 | 8 | 11 | 11 | 11 | 11 | 15 | 14 | 11 | 11 | 10 | 9 |
| Cloudy days (≥ 70%) | 15 | 14 | 14 | 11 | 12 | 9 | 12 | 13 | 10 | 9 | 10 | 14 |
| Relative humidity (%) | 84 | 83 | 84 | 84 | 85 | 85 | 86 | 86 | 83 | 80 | 80 | 81 |
| Wind speed (m/s) | 3.6 | 3.8 | 3.8 | 4.0 | 4.0 | 3.9 | 3.3 | 3.3 | 3.0 | 3.0 | 3.2 | 3.8 |
| Jan – Jun | Jan | Feb | Mar | Apr | May | Jun |
|---|---|---|---|---|---|---|
| Cloud cover (%) | 60 | 61 | 60 | 55 | 54 | 48 |
| Clear days (≤ 30% cloud) | 7 | 6 | 7 | 8 | 8 | 10 |
| Partly cloudy days (30–70%) | 9 | 8 | 11 | 11 | 11 | 11 |
| Cloudy days (≥ 70%) | 15 | 14 | 14 | 11 | 12 | 9 |
| Relative humidity (%) | 84 | 83 | 84 | 84 | 85 | 85 |
| Wind speed (m/s) | 3.6 | 3.8 | 3.8 | 4.0 | 4.0 | 3.9 |
| Jul – Dec | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|
| Cloud cover (%) | 58 | 59 | 51 | 47 | 51 | 57 |
| Clear days (≤ 30% cloud) | 4 | 4 | 9 | 11 | 10 | 8 |
| Partly cloudy days (30–70%) | 15 | 14 | 11 | 11 | 10 | 9 |
| Cloudy days (≥ 70%) | 12 | 13 | 10 | 9 | 10 | 14 |
| Relative humidity (%) | 86 | 86 | 83 | 80 | 80 | 81 |
| Wind speed (m/s) | 3.3 | 3.3 | 3.0 | 3.0 | 3.2 | 3.8 |
Methodology & sources
Temperature & precipitation — the official 1991–2020 climate normals from NOAA's U.S. Climate Normals, measured at Redwood City (NOAA GHCN station USC00047339), about 10 km from the city centre.
Cloud, humidity, wind & sunshine — modelled estimates from NASA POWER, NASA's satellite-and-reanalysis climatology. This is the standard global source for atmospheric variables, which are not measured at most weather stations.