| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 39°F | 58°F | 48°F | 3.3" |
| February | 43°F | 62°F | 52°F | 3.0" |
| March | 45°F | 67°F | 54°F | 1.8" |
| April | 47°F | 71°F | 57°F | 1.9" |
| May | 52°F | 78°F | 63°F | 0.6" |
| June | 56°F | 85°F | 68°F | 0.0" |
| July | 58°F | 90°F | 71°F | 0.0" |
| August | 57°F | 90°F | 70°F | 0.0" |
| September | 56°F | 86°F | 68°F | 0.0" |
| October | 50°F | 77°F | 62°F | 1.4" |
| November | 45°F | 68°F | 55°F | 1.2" |
| December | 40°F | 57°F | 47°F | 2.3" |
| Index | Hercules | California | National |
| Air quality index | 40 | 55 | 42 |
| Pollution index | 19,202,400 | 10,473,190 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 290 |
| Days with moderate air quality | 74 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.180% |
| Benzene | 0.140% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.280% |
| Mercury | 0.060% |
| City | Population | Air Quality Index | National Avg. |
| Port Costa, CA | 242 | 40 | 20.0% |
| Berkeley, CA | 123,065 | 40 | 20.0% |
| Kensington, CA | 5,171 | 40 | 20.0% |
| Richmond, CA | 110,051 | 40 | 20.0% |
| Walnut Creek, CA | 69,836 | 40 | 20.0% |
| Hercules, CA | 26,090 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Neenah, WI | 26,083 | 37 | 26.0% |
| Milford, MA | 26,072 | 40 | 20.0% |
| Wethersfield, CT | 26,068 | 41 | 18.0% |
| Bessemer, AL | 26,063 | 53 | 6.0% |
| West Odessa, TX | 26,117 | 28 | 44.0% |
| Hercules, CA | 26,090 | 40 | 20.0% |
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