| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 26°F | 39°F | 32°F | 5.5" |
| February | 23°F | 37°F | 30°F | 2.2" |
| March | 29°F | 45°F | 36°F | 6.7" |
| April | 37°F | 51°F | 44°F | 7.9" |
| May | 47°F | 60°F | 53°F | 6.7" |
| June | 57°F | 71°F | 63°F | 1.4" |
| July | 63°F | 77°F | 70°F | 5.0" |
| August | 64°F | 79°F | 71°F | 1.8" |
| September | 59°F | 74°F | 66°F | 4.9" |
| October | 51°F | 64°F | 57°F | 5.6" |
| November | 39°F | 54°F | 47°F | 4.6" |
| December | 30°F | 43°F | 36°F | 5.5" |
| Index | Chatham | Massachusetts | National |
| Air quality index | 36 | 40 | 42 |
| Pollution index | 7,903,830 | 8,399,610 | 2,726,193 |
| Measurement | Total |
| Days measured | 359 |
| Days with good air quality | 348 |
| Days with moderate air quality | 11 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.060% |
| Benzene | 0.070% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.080% |
| Mercury | 0.030% |
| City | Population | Air Quality Index | National Avg. |
| West Chatham, MA | 1,224 | 36 | 28.0% |
| East Dennis, MA | 3,068 | 36 | 28.0% |
| Northwest Harwich, MA | 4,123 | 36 | 28.0% |
| South Yarmouth, MA | 10,598 | 36 | 28.0% |
| Brewster, MA | 1,347 | 36 | 28.0% |
| Chatham, MA | 1,550 | 36 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| Union Point, GA | 1,550 | 44 | 12.0% |
| Manning, IA | 1,550 | 40 | 20.0% |
| Falmouth Foreside, ME | 1,550 | 40 | 20.0% |
| Homer, MI | 1,550 | 38 | 24.0% |
| Sackets Harbor, NY | 1,550 | 35 | 30.0% |
| Chatham, MA | 1,550 | 36 | 28.0% |
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