| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 41°F | 57°F | 48°F | 9.3" |
| February | 44°F | 62°F | 52°F | 3.6" |
| March | 47°F | 66°F | 55°F | 3.0" |
| April | 49°F | 70°F | 58°F | 1.8" |
| May | 52°F | 75°F | 62°F | 0.0" |
| June | 56°F | 81°F | 66°F | 0.0" |
| July | 57°F | 83°F | 67°F | 0.2" |
| August | 57°F | 83°F | 67°F | 0.0" |
| September | 57°F | 84°F | 68°F | 0.1" |
| October | 53°F | 76°F | 63°F | 0.6" |
| November | 46°F | 65°F | 54°F | 0.8" |
| December | 40°F | 57°F | 47°F | 3.3" |
| Index | Fairfield | California | National |
| Air quality index | 35 | 55 | 42 |
| Pollution index | 2,457,150 | 10,473,190 | 2,726,193 |
| Measurement | Total |
| Days measured | 363 |
| Days with good air quality | 330 |
| Days with moderate air quality | 31 |
| Days w/ poor A.Q. for sensitive groups | 2 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.080% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.010% |
| Mercury | 0.020% |
| City | Population | Air Quality Index | National Avg. |
| Green Valley, CA | 1,583 | 35 | 30.0% |
| Napa, CA | 78,294 | 35 | 30.0% |
| Vacaville, CA | 99,958 | 35 | 30.0% |
| Hartley, CA | 2,655 | 35 | 30.0% |
| Elmira, CA | 234 | 35 | 30.0% |
| Fairfield, CA | 116,544 | 35 | 30.0% |
| City | Population | Air Quality Index | National Avg. |
| Provo, UT | 116,886 | 46 | 8.0% |
| Clearwater, FL | 115,975 | 43 | 14.0% |
| Rochester, MN | 117,134 | 36 | 28.0% |
| Independence, MO | 117,139 | 47 | 6.0% |
| Brandon, FL | 115,909 | 43 | 14.0% |
| Fairfield, CA | 116,544 | 35 | 30.0% |
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