| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 9°F | 28°F | 19°F | 2.1" |
| February | 11°F | 30°F | 20°F | 2.5" |
| March | 19°F | 39°F | 29°F | 2.7" |
| April | 32°F | 55°F | 43°F | 3.3" |
| May | 43°F | 68°F | 55°F | 4.3" |
| June | 52°F | 75°F | 63°F | 6.0" |
| July | 57°F | 79°F | 68°F | 5.5" |
| August | 55°F | 78°F | 66°F | 4.0" |
| September | 48°F | 71°F | 59°F | 3.3" |
| October | 38°F | 58°F | 47°F | 5.2" |
| November | 27°F | 46°F | 36°F | 2.7" |
| December | 17°F | 33°F | 25°F | 3.6" |
| Index | Williamstown | Vermont | National |
| Air quality index | 34 | 36 | 42 |
| Pollution index | 1,278,430 | 1,478,772 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 328 |
| Days with moderate air quality | 37 |
| Days w/ poor A.Q. for sensitive groups | |
| Days with unhealthy air quality |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.010% |
| Mercury | 0.001% |
| City | Population | Air Quality Index | National Avg. |
| Chelsea, VT | 463 | 34 | 32.0% |
| South Barre, VT | 1,110 | 34 | 32.0% |
| East Barre, VT | 807 | 34 | 32.0% |
| Websterville, VT | 380 | 34 | 32.0% |
| Barre, VT | 8,590 | 34 | 32.0% |
| Williamstown, VT | 1,253 | 34 | 32.0% |
| City | Population | Air Quality Index | National Avg. |
| Galena, IN | 1,253 | 49 | 2.0% |
| Edina, MO | 1,253 | 41 | 18.0% |
| Walnut, MS | 1,253 | 39 | 22.0% |
| Creighton, NE | 1,253 | 35 | 30.0% |
| Munday, TX | 1,253 | 26 | 48.0% |
| Williamstown, VT | 1,253 | 34 | 32.0% |
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