| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 21°F | 45°F | 31°F | 1.8" |
| February | 22°F | 46°F | 32°F | 2.0" |
| March | 30°F | 58°F | 42°F | 2.1" |
| April | 35°F | 63°F | 47°F | 4.0" |
| May | 44°F | 70°F | 55°F | 5.2" |
| June | 54°F | 84°F | 68°F | 4.6" |
| July | 60°F | 89°F | 73°F | 5.7" |
| August | 59°F | 87°F | 71°F | 4.5" |
| September | 51°F | 79°F | 63°F | 5.7" |
| October | 39°F | 67°F | 51°F | 4.1" |
| November | 29°F | 56°F | 41°F | 2.2" |
| December | 19°F | 44°F | 30°F | 2.9" |
| Index | Thornton | Colorado | National |
| Air quality index | 58 | 38 | 50 |
| Pollution index | 209,253 | 2,034,619 | 5,066,862 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 91 |
| Days with moderate air quality | 252 |
| Days w/ poor A.Q. for sensitive groups | 20 |
| Days with unhealthy air quality | 2 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.003% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City, State | Population | Air Quality Index | National Avg. |
| Eldorado Springs, CO | 935 | 47 | 6% |
| Erie, CO | 20,801 | 47 | 6% |
| Louisville, CO | 19,972 | 47 | 6% |
| Superior, CO | 12,928 | 47 | 6% |
| Gunbarrel, CO | 9,559 | 47 | 6% |
| Thornton, CO | 130,511 | 58 | 16% |
| City, State | Population | Air Quality Index | National Avg. |
| New Haven, CT | 130,405 | 41 | 18% |
| Waco, TX | 130,659 | 38 | 24% |
| Charleston, SC | 129,888 | 38 | 24% |
| Enterprise, NV | 129,620 | 54 | 8% |
| Cedar Rapids, IA | 129,537 | 39 | 22% |
| Thornton, CO | 130,511 | 58 | 16% |
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