| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 26°F | 41°F | 33°F | 4.1" |
| February | 25°F | 40°F | 33°F | 4.0" |
| March | 31°F | 45°F | 38°F | 3.9" |
| April | 40°F | 55°F | 47°F | 3.7" |
| May | 49°F | 64°F | 55°F | 3.8" |
| June | 57°F | 72°F | 64°F | 3.5" |
| July | 65°F | 80°F | 72°F | 3.4" |
| August | 63°F | 79°F | 71°F | 3.8" |
| September | 58°F | 73°F | 65°F | 3.5" |
| October | 49°F | 63°F | 56°F | 4.9" |
| November | 39°F | 54°F | 47°F | 4.3" |
| December | 31°F | 46°F | 39°F | 4.6" |
| Index | Harwich Port | 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 | 1,259 | 36 | 28.0% |
| Dennis, MA | 2,003 | 36 | 28.0% |
| Harwich Center, MA | 1,431 | 36 | 28.0% |
| Yarmouth Port, MA | 5,330 | 36 | 28.0% |
| Barnstable Town, MA | 45,771 | 36 | 28.0% |
| Harwich Port, MA | 1,962 | 36 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| Newtown, CT | 1,962 | 43 | 14.0% |
| New Athens, IL | 1,961 | 54 | 8.0% |
| Belleville, KS | 1,961 | 32 | 36.0% |
| Pelahatchie, MS | 1,961 | 44 | 12.0% |
| Mayville, ND | 1,961 | 33 | 34.0% |
| Harwich Port, MA | 1,962 | 36 | 28.0% |