| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 23°F | 39°F | 31°F | 5.1" |
| February | 21°F | 37°F | 29°F | 3.7" |
| March | 26°F | 44°F | 36°F | 7.9" |
| April | 36°F | 55°F | 46°F | 10.1" |
| May | 46°F | 65°F | 55°F | 5.8" |
| June | 57°F | 75°F | 65°F | 4.6" |
| July | 62°F | 80°F | 70°F | 3.4" |
| August | 63°F | 81°F | 71°F | 4.1" |
| September | 57°F | 76°F | 66°F | 5.3" |
| October | 49°F | 65°F | 56°F | 9.3" |
| November | 35°F | 54°F | 45°F | 6.2" |
| December | 26°F | 41°F | 33°F | 5.6" |
| Index | Westerly | Rhode Island | National |
| Air quality index | 37 | 45 | 42 |
| Pollution index | 2,960,790 | 3,440,259 | 2,726,193 |
| Measurement | Total |
| Days measured | 364 |
| Days with good air quality | 323 |
| Days with moderate air quality | 34 |
| Days w/ poor A.Q. for sensitive groups | 7 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.003% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.020% |
| Mercury | 0.005% |
| City | Population | Air Quality Index | National Avg. |
| Mashantucket, CT | 225 | 37 | 26.0% |
| Old Mystic, CT | 3,302 | 37 | 26.0% |
| Charlestown, RI | 1,392 | 37 | 26.0% |
| Misquamicut, RI | 378 | 37 | 26.0% |
| Noank, CT | 1,454 | 37 | 26.0% |
| Westerly, RI | 17,842 | 37 | 26.0% |
| City | Population | Air Quality Index | National Avg. |
| Radford, VA | 17,833 | 41 | 18.0% |
| Jenison, MI | 17,851 | 38 | 24.0% |
| El Dorado, AR | 17,826 | 35 | 30.0% |
| Canby, OR | 17,860 | 38 | 24.0% |
| Amsterdam, NY | 17,823 | 37 | 26.0% |
| Westerly, RI | 17,842 | 37 | 26.0% |
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