| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 25°F | 40°F | 31°F | 7.2" |
| February | 22°F | 38°F | 29°F | 3.1" |
| March | 27°F | 44°F | 35°F | 9.7" |
| April | 36°F | 54°F | 45°F | 8.7" |
| May | 46°F | 62°F | 53°F | 6.7" |
| June | 57°F | 73°F | 64°F | 1.9" |
| July | 64°F | 79°F | 71°F | 5.2" |
| August | 63°F | 81°F | 71°F | 3.1" |
| September | 57°F | 75°F | 66°F | 9.5" |
| October | 48°F | 65°F | 56°F | 7.3" |
| November | 36°F | 54°F | 45°F | 5.9" |
| December | 27°F | 42°F | 34°F | 5.5" |
| Index | South Dennis | 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. |
| Orleans, MA | 1,519 | 36 | 28.0% |
| Brewster, MA | 1,347 | 36 | 28.0% |
| East Harwich, MA | 4,756 | 36 | 28.0% |
| Northwest Harwich, MA | 4,123 | 36 | 28.0% |
| West Dennis, MA | 2,479 | 36 | 28.0% |
| South Dennis, MA | 2,895 | 36 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| Milaca, MN | 2,894 | 32 | 36.0% |
| Claryville, KY | 2,896 | 54 | 8.0% |
| Lake Wissota, WI | 2,896 | 34 | 32.0% |
| Palo Cedro, CA | 2,893 | 42 | 16.0% |
| Deer Lodge, MT | 2,893 | 20 | 60.0% |
| South Dennis, MA | 2,895 | 36 | 28.0% |
Here are the best places to live in Massachusetts
See the best places to live in South Dennis
Most Dangerous Cities In The US
These are the largest cities in Massachusetts