| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 22°F | 40°F | 30°F | 3.3" |
| February | 23°F | 42°F | 32°F | 2.7" |
| March | 35°F | 57°F | 45°F | 4.6" |
| April | 44°F | 69°F | 56°F | 6.0" |
| May | 53°F | 76°F | 64°F | 5.0" |
| June | 62°F | 84°F | 73°F | 6.1" |
| July | 64°F | 86°F | 75°F | 4.9" |
| August | 62°F | 86°F | 73°F | 3.0" |
| September | 55°F | 80°F | 66°F | 3.6" |
| October | 44°F | 68°F | 55°F | 4.1" |
| November | 33°F | 56°F | 44°F | 3.5" |
| December | 26°F | 44°F | 35°F | 4.4" |
| Index | Williams | Indiana | National |
| Air quality index | 42 | 56 | 42 |
| Pollution index | 809,095 | 2,719,453 | 2,726,193 |
| Measurement | Total |
| Days measured | 363 |
| Days with good air quality | 291 |
| Days with moderate air quality | 72 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.002% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.110% |
| Mercury | 0.080% |
| City | Population | Air Quality Index | National Avg. |
| Scotland, IN | 146 | 1 | 98.0% |
| Crane, IN | 326 | 1 | 98.0% |
| Dover Hill, IN | 16 | 1 | 98.0% |
| Shoals, IN | 720 | 1 | 98.0% |
| Loogootee, IN | 2,579 | 1 | 98.0% |
| Williams, IN | 200 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Grayling, AK | 200 | 31 | 38.0% |
| Port Alsworth, AK | 200 | 31 | 38.0% |
| Lockhart, AL | 200 | 31 | 38.0% |
| Ellenton, GA | 200 | 35 | 30.0% |
| Burr Oak, IA | 200 | 35 | 30.0% |
| Williams, IN | 200 | 42 | 16.0% |
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