| 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 | Northwest Harwich | 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. |
| Barnstable Town, MA | 44,497 | 36 | 28.0% |
| Dennis Port, MA | 3,523 | 36 | 28.0% |
| Harwich Port, MA | 1,906 | 36 | 28.0% |
| South Yarmouth, MA | 10,598 | 36 | 28.0% |
| North Eastham, MA | 1,741 | 36 | 28.0% |
| Northwest Harwich, MA | 4,123 | 36 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| Dewey-Humboldt, AZ | 4,123 | 43 | 14.0% |
| Randleman, NC | 4,124 | 40 | 20.0% |
| Waverly, TN | 4,124 | 40 | 20.0% |
| Jefferson, IA | 4,121 | 37 | 26.0% |
| Burnham, IL | 4,121 | 55 | 10.0% |
| Northwest Harwich, MA | 4,123 | 36 | 28.0% |
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