| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 23°F | 41°F | 32°F | 3.3" |
| February | 23°F | 42°F | 32°F | 3.6" |
| March | 30°F | 50°F | 39°F | 4.0" |
| April | 41°F | 62°F | 50°F | 4.3" |
| May | 50°F | 71°F | 59°F | 3.9" |
| June | 60°F | 80°F | 69°F | 4.9" |
| July | 67°F | 85°F | 76°F | 3.5" |
| August | 66°F | 84°F | 74°F | 4.2" |
| September | 59°F | 78°F | 68°F | 3.8" |
| October | 48°F | 67°F | 57°F | 4.7" |
| November | 38°F | 56°F | 47°F | 3.0" |
| December | 29°F | 46°F | 38°F | 5.4" |
| Index | Westport | Connecticut | National |
| Air quality index | 43 | 43 | 42 |
| Pollution index | 16,950,700 | 8,629,883 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 262 |
| Days with moderate air quality | 82 |
| Days w/ poor A.Q. for sensitive groups | 18 |
| Days with unhealthy air quality | 3 |
| Pollutant | Total |
| Arsenic | 0.030% |
| Benzene | 0.140% |
| Carbon Tetrachloride | 0.070% |
| Lead | 0.080% |
| Mercury | 0.030% |
| City | Population | Air Quality Index | National Avg. |
| Derby, CT | 12,420 | 41 | 18.0% |
| Shelton, CT | 41,162 | 41 | 18.0% |
| Darien, CT | 21,519 | 43 | 14.0% |
| Norwalk, CT | 88,755 | 43 | 14.0% |
| Southport, CT | 1,710 | 43 | 14.0% |
| Westport, CT | 27,511 | 43 | 14.0% |
| City | Population | Air Quality Index | National Avg. |
| King, ON | 27,487 | n/a | |
| Millville, NJ | 27,485 | 40 | 20.0% |
| Danvers, MA | 27,549 | 43 | 14.0% |
| Wasco, CA | 27,553 | 67 | 34.0% |
| Yukon, OK | 27,557 | 48 | 4.0% |
| Westport, CT | 27,511 | 43 | 14.0% |
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