| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 24°F | 39°F | 31°F | 6.8" |
| February | 23°F | 39°F | 30°F | 6.4" |
| March | 29°F | 46°F | 37°F | 7.5" |
| April | 38°F | 56°F | 47°F | 9.7" |
| May | 48°F | 65°F | 56°F | 6.2" |
| June | 58°F | 73°F | 65°F | 8.0" |
| July | 64°F | 79°F | 72°F | 9.7" |
| August | 62°F | 77°F | 69°F | 9.2" |
| September | 55°F | 70°F | 62°F | 14.3" |
| October | 45°F | 61°F | 53°F | 4.9" |
| November | 38°F | 52°F | 45°F | 10.3" |
| December | 28°F | 44°F | 36°F | 7.1" |
| Index | Onset | Massachusetts | National |
| Air quality index | 36 | 40 | 42 |
| Pollution index | 9,737,620 | 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 | 0.180% |
| Benzene | 0.070% |
| Carbon Tetrachloride | 0.040% |
| Lead | 0.170% |
| Mercury | 0.140% |
| City | Population | Air Quality Index | National Avg. |
| Marion Center, MA | 1,061 | 36 | 28.0% |
| Pocasset, MA | 2,596 | 36 | 28.0% |
| Seconsett Island, MA | 37 | 36 | 28.0% |
| West Wareham, MA | 2,398 | 36 | 28.0% |
| Bourne, MA | 1,377 | 36 | 28.0% |
| Onset, MA | 1,049 | 36 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| Skyline, AL | 1,049 | 44 | 12.0% |
| Herald, CA | 1,049 | 45 | 10.0% |
| Saybrook Manor, CT | 1,049 | 37 | 26.0% |
| Canon, GA | 1,049 | 41 | 18.0% |
| Tyrone, OK | 1,049 | 15 | 70.0% |
| Onset, MA | 1,049 | 36 | 28.0% |
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