| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 21°F | 37°F | 28°F | 5.0" |
| February | 19°F | 35°F | 26°F | 9.8" |
| March | 25°F | 44°F | 34°F | 6.0" |
| April | 38°F | 59°F | 47°F | 15.0" |
| May | 46°F | 68°F | 56°F | 14.6" |
| June | 58°F | 78°F | 67°F | 11.3" |
| July | 62°F | 81°F | 70°F | 12.6" |
| August | 62°F | 82°F | 71°F | 8.3" |
| September | 55°F | 76°F | 65°F | 2.3" |
| October | 48°F | 64°F | 54°F | 12.4" |
| November | 34°F | 51°F | 41°F | 5.2" |
| December | 23°F | 36°F | 29°F | 5.5" |
| Index | Derby | Connecticut | National |
| Air quality index | 41 | 43 | 50 |
| Pollution index | 14,500,300 | 7,127,531 | 5,066,862 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 280 |
| Days with moderate air quality | 71 |
| Days w/ poor A.Q. for sensitive groups | 12 |
| Days with unhealthy air quality | 2 |
| Pollutant | Total |
| Arsenic | 0.030% |
| Benzene | 0.140% |
| Carbon Tetrachloride | 0.050% |
| Lead | 0.080% |
| Mercury | 0.060% |
| City, State | Population | Air Quality Index | National Avg. |
| Cheshire Village, CT | 6,103 | 41 | 18% |
| West Haven, CT | 54,972 | 41 | 18% |
| Ansonia, CT | 18,950 | 41 | 18% |
| Heritage Village, CT | 3,875 | 41 | 18% |
| North Haven, CT | 23,888 | 41 | 18% |
| Derby, CT | 12,755 | 41 | 18% |
| City, State | Population | Air Quality Index | National Avg. |
| Kewanee, IL | 12,755 | 41 | 18% |
| Auburn, IN | 12,758 | 45 | 10% |
| St. Marys, PA | 12,748 | 35 | 30% |
| Parker, SC | 12,743 | 46 | 8% |
| Short Hills, NJ | 12,771 | 51 | 2% |
| Derby, CT | 12,755 | 41 | 18% |
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