| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 24°F | 42°F | 32°F | 3.4" |
| February | 25°F | 44°F | 33°F | 2.6" |
| March | 34°F | 56°F | 44°F | 3.9" |
| April | 43°F | 69°F | 56°F | 4.2" |
| May | 52°F | 76°F | 63°F | 4.1" |
| June | 60°F | 83°F | 71°F | 4.9" |
| July | 64°F | 85°F | 74°F | 4.8" |
| August | 63°F | 86°F | 73°F | 3.6" |
| September | 56°F | 80°F | 67°F | 3.2" |
| October | 45°F | 68°F | 55°F | 3.7" |
| November | 35°F | 57°F | 45°F | 2.9" |
| December | 29°F | 46°F | 37°F | 4.2" |
| Index | Williamstown | West Virginia | National |
| Air quality index | 35 | 126 | 42 |
| Pollution index | 2,805,740 | 1,996,538 | 2,726,193 |
| Measurement | Total |
| Days measured | 364 |
| Days with good air quality | 333 |
| Days with moderate air quality | 31 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.005% |
| Lead | 0.060% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| North Hills, WV | 950 | 35 | 30.0% |
| Newport CDP (Shelby County), OH | 159 | 35 | 30.0% |
| Parkersburg, WV | 29,732 | 35 | 30.0% |
| Belmont, WV | 965 | 35 | 30.0% |
| Lowell, OH | 538 | 35 | 30.0% |
| Williamstown, WV | 2,901 | 35 | 30.0% |
| City | Population | Air Quality Index | National Avg. |
| Pretty Bayou, FL | 2,901 | 38 | 24.0% |
| Port Richey, FL | 2,900 | 43 | 14.0% |
| Butler, AL | 2,902 | 36 | 28.0% |
| Tangelo Park, FL | 2,899 | 39 | 22.0% |
| Poplarville, MS | 2,899 | 35 | 30.0% |
| Williamstown, WV | 2,901 | 35 | 30.0% |
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