| 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 | Millbrae | California | National |
| Air quality index | 43 | 55 | 50 |
| Pollution index | 9,645,610 | 18,106,726 | 5,066,862 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 252 |
| Days with moderate air quality | 101 |
| Days w/ poor A.Q. for sensitive groups | 10 |
| Days with unhealthy air quality | 2 |
| Pollutant | Total |
| Arsenic | 0.140% |
| Benzene | 0.070% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.100% |
| Mercury | 0.020% |
| City, State | Population | Air Quality Index | National Avg. |
| San Lorenzo, CA | 24,790 | 40 | 20% |
| Brisbane, CA | 4,568 | 40 | 20% |
| Daly City, CA | 105,543 | 40 | 20% |
| South San Francisco, CA | 66,587 | 40 | 20% |
| Oakland, CA | 412,040 | 40 | 20% |
| Millbrae, CA | 22,522 | 43 | 14% |
| City, State | Population | Air Quality Index | National Avg. |
| Gallup, NM | 22,523 | 17 | 66% |
| Jacksonville Beach, FL | 22,519 | 43 | 14% |
| Garden City, NY | 22,531 | 51 | 2% |
| Horizon West, FL | 22,538 | 39 | 22% |
| Hastings, MN | 22,501 | 37 | 26% |
| Millbrae, CA | 22,522 | 43 | 14% |
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