| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 41°F | 59°F | 50°F | 2.8" |
| February | 45°F | 62°F | 53°F | 3.1" |
| March | 47°F | 65°F | 55°F | 2.9" |
| April | 49°F | 67°F | 57°F | 1.8" |
| May | 52°F | 69°F | 59°F | 0.4" |
| June | 54°F | 72°F | 62°F | 0.3" |
| July | 56°F | 73°F | 63°F | 0.0" |
| August | 57°F | 73°F | 63°F | 0.0" |
| September | 55°F | 76°F | 64°F | 0.1" |
| October | 52°F | 73°F | 61°F | 1.0" |
| November | 47°F | 65°F | 56°F | 1.9" |
| December | 42°F | 59°F | 50°F | 4.1" |
| Index | Piedmont | 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. |
| Hercules, CA | 26,090 | 40 | 20.0% |
| East Richmond Heights, CA | 3,473 | 40 | 20.0% |
| Montalvin Manor, CA | 2,490 | 40 | 20.0% |
| Rollingwood, CA | 3,612 | 40 | 20.0% |
| Santa Venetia, CA | 3,891 | 40 | 20.0% |
| Piedmont, CA | 11,454 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Lyndon, KY | 11,451 | 49 | 2.0% |
| Madison Heights, VA | 11,447 | 26 | 48.0% |
| Elizabethtown, PA | 11,445 | 41 | 18.0% |
| Milford, DE | 11,463 | 42 | 16.0% |
| Magalia, CA | 11,444 | 46 | 8.0% |
| Piedmont, CA | 11,454 | 40 | 20.0% |
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