| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 18°F | 38°F | 28°F | 3.3" |
| February | 18°F | 40°F | 29°F | 3.6" |
| March | 26°F | 50°F | 38°F | 3.6" |
| April | 37°F | 65°F | 50°F | 4.0" |
| May | 47°F | 75°F | 60°F | 4.0" |
| June | 57°F | 82°F | 69°F | 5.5" |
| July | 63°F | 88°F | 75°F | 4.9" |
| August | 60°F | 86°F | 72°F | 4.9" |
| September | 54°F | 80°F | 66°F | 3.9" |
| October | 43°F | 67°F | 54°F | 5.9" |
| November | 32°F | 55°F | 43°F | 3.2" |
| December | 24°F | 44°F | 33°F | 4.5" |
| Index | Collinsville | Connecticut | National |
| Air quality index | 37 | 43 | 42 |
| Pollution index | 7,859,360 | 8,629,883 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 342 |
| Days with moderate air quality | 23 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.030% |
| Benzene | 0.070% |
| Carbon Tetrachloride | 0.030% |
| Lead | 0.320% |
| Mercury | 0.070% |
| City | Population | Air Quality Index | National Avg. |
| Bristol, CT | 60,039 | 37 | 26.0% |
| Terryville, CT | 5,019 | 37 | 26.0% |
| Northwest Harwinton, CT | 2,897 | 37 | 26.0% |
| Norfolk, CT | 639 | 37 | 26.0% |
| Winsted, CT | 6,504 | 37 | 26.0% |
| Collinsville, CT | 3,729 | 37 | 26.0% |
| City | Population | Air Quality Index | National Avg. |
| San Andreas, CA | 3,729 | 39 | 22.0% |
| Shenandoah Farms, VA | 3,729 | 38 | 24.0% |
| La Cienega, NM | 3,728 | 44 | 12.0% |
| Saxon, SC | 3,727 | 44 | 12.0% |
| Warminster Heights, PA | 3,726 | 51 | 2.0% |
| Collinsville, CT | 3,729 | 37 | 26.0% |
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