| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 25°F | 46°F | 34°F | 3.6" |
| February | 26°F | 48°F | 36°F | 3.1" |
| March | 35°F | 60°F | 46°F | 4.3" |
| April | 45°F | 72°F | 58°F | 4.6" |
| May | 52°F | 78°F | 65°F | 4.9" |
| June | 61°F | 86°F | 73°F | 4.6" |
| July | 65°F | 87°F | 75°F | 6.8" |
| August | 63°F | 87°F | 74°F | 3.6" |
| September | 57°F | 82°F | 68°F | 3.5" |
| October | 45°F | 70°F | 57°F | 3.7" |
| November | 35°F | 60°F | 46°F | 3.0" |
| December | 29°F | 49°F | 38°F | 4.4" |
| Index | Williamson | West Virginia | National |
| Air quality index | 42 | 126 | 42 |
| Pollution index | 780,751 | 1,996,538 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 299 |
| Days with moderate air quality | 66 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Verdunville, WV | 417 | 40 | 20.0% |
| Mount Gay-Shamrock, WV | 1,434 | 40 | 20.0% |
| Omar, WV | 367 | 40 | 20.0% |
| Holden, WV | 677 | 40 | 20.0% |
| Belfry, KY | 261 | 42 | 16.0% |
| Williamson, WV | 2,735 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Albany, MN | 2,735 | 32 | 36.0% |
| Saint-Gilles, QC | 2,735 | n/a | |
| Hawthorne, NV | 2,734 | 13 | 74.0% |
| French River / Rivière des Français, ON | 2,734 | n/a | |
| Wendell, ID | 2,736 | 20 | 60.0% |
| Williamson, WV | 2,735 | 42 | 16.0% |
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