| 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 | 42 |
| Pollution index | 209,253 | 2,068,342 | 2,726,193 |
| 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 | Population | Air Quality Index | National Avg. |
| Lafayette, CO | 27,952 | 47 | 6.0% |
| Paragon Estates, CO | 785 | 47 | 6.0% |
| Broomfield, CO | 69,444 | 47 | 6.0% |
| Dacono, CO | 6,167 | 47 | 6.0% |
| Valmont, CO | 98 | 47 | 6.0% |
| Thornton, CO | 144,186 | 58 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Torrance, CA | 144,430 | 72 | 44.0% |
| Bridgeport, CT | 145,014 | 43 | 14.0% |
| Saguenay, QC | 145,134 | n/a | |
| Paterson, NJ | 145,484 | 51 | 2.0% |
| Savannah, GA | 145,492 | 39 | 22.0% |
| Thornton, CO | 144,186 | 58 | 16.0% |
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