| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 44°F | 58°F | 51°F | 3.2" |
| February | 46°F | 62°F | 53°F | 3.4" |
| March | 47°F | 64°F | 54°F | 2.7" |
| April | 49°F | 67°F | 56°F | 1.7" |
| May | 51°F | 69°F | 58°F | 0.3" |
| June | 54°F | 72°F | 61°F | 0.2" |
| July | 56°F | 73°F | 62°F | 0.0" |
| August | 56°F | 73°F | 62°F | 0.0" |
| September | 56°F | 76°F | 63°F | 0.1" |
| October | 54°F | 73°F | 62°F | 1.0" |
| November | 49°F | 65°F | 56°F | 1.7" |
| December | 44°F | 58°F | 51°F | 4.4" |
| Index | Belmont | California | National |
| Air quality index | 43 | 55 | 42 |
| Pollution index | 9,645,610 | 10,473,190 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 263 |
| Days with moderate air quality | 98 |
| Days w/ poor A.Q. for sensitive groups | 4 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.140% |
| Benzene | 0.070% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.100% |
| Mercury | 0.020% |
| City | Population | Air Quality Index | National Avg. |
| Castro Valley, CA | 64,392 | 40 | 20.0% |
| Colma, CA | 1,492 | 40 | 20.0% |
| South San Francisco, CA | 66,878 | 40 | 20.0% |
| San Leandro, CA | 90,489 | 40 | 20.0% |
| Brisbane, CA | 4,645 | 40 | 20.0% |
| Belmont, CA | 26,963 | 43 | 14.0% |
| City | Population | Air Quality Index | National Avg. |
| Marshalltown, IA | 26,957 | 37 | 26.0% |
| Bristol, TN | 26,973 | 45 | 10.0% |
| Eureka, CA | 26,938 | 27 | 46.0% |
| Maryland Heights, MO | 26,996 | 54 | 8.0% |
| West Chicago, IL | 26,998 | 55 | 10.0% |
| Belmont, CA | 26,963 | 43 | 14.0% |
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