| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 38°F | 58°F | 47°F | 3.3" |
| February | 41°F | 63°F | 51°F | 3.1" |
| March | 44°F | 68°F | 55°F | 2.9" |
| April | 47°F | 74°F | 59°F | 1.8" |
| May | 52°F | 82°F | 65°F | 0.5" |
| June | 57°F | 90°F | 71°F | 0.3" |
| July | 59°F | 95°F | 74°F | 0.0" |
| August | 58°F | 93°F | 73°F | 0.0" |
| September | 56°F | 90°F | 70°F | 0.1" |
| October | 50°F | 79°F | 63°F | 1.2" |
| November | 43°F | 66°F | 53°F | 1.6" |
| December | 38°F | 57°F | 47°F | 3.8" |
| Index | Thornton | California | National |
| Air quality index | 45 | 55 | 42 |
| Pollution index | 15,476,500 | 10,473,190 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 229 |
| Days with moderate air quality | 123 |
| Days w/ poor A.Q. for sensitive groups | 12 |
| Days with unhealthy air quality | 1 |
| Pollutant | Total |
| Arsenic | 0.090% |
| Benzene | 0.130% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.130% |
| Mercury | 0.070% |
| City | Population | Air Quality Index | National Avg. |
| Acampo, CA | 261 | 45 | 10.0% |
| Galt, CA | 26,235 | 45 | 10.0% |
| Victor, CA | 420 | 45 | 10.0% |
| Woodbridge, CA | 3,806 | 45 | 10.0% |
| Bethel Island, CA | 2,015 | 45 | 10.0% |
| Thornton, CA | 903 | 45 | 10.0% |
| City | Population | Air Quality Index | National Avg. |
| Teviston, CA | 903 | 66 | 32.0% |
| Mars Hill, ME | 903 | 31 | 38.0% |
| Deckerville, MI | 903 | 26 | 48.0% |
| Mountainair, NM | 903 | 53 | 6.0% |
| South Lebanon, OR | 903 | 28 | 44.0% |
| Thornton, CA | 903 | 45 | 10.0% |
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