| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 20°F | 38°F | 29°F | 2.3" |
| February | 21°F | 40°F | 30°F | 2.2" |
| March | 31°F | 53°F | 41°F | 3.9" |
| April | 41°F | 66°F | 53°F | 3.6" |
| May | 50°F | 75°F | 63°F | 4.0" |
| June | 59°F | 83°F | 71°F | 5.2" |
| July | 62°F | 84°F | 73°F | 4.3" |
| August | 60°F | 84°F | 71°F | 3.6" |
| September | 53°F | 78°F | 65°F | 3.2" |
| October | 42°F | 67°F | 53°F | 3.3" |
| November | 32°F | 55°F | 42°F | 2.6" |
| December | 26°F | 43°F | 34°F | 3.6" |
| Index | Thornville | Ohio | National |
| Air quality index | 46 | 40 | 42 |
| Pollution index | 3,612,840 | 4,472,386 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 237 |
| Days with moderate air quality | 127 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.004% |
| Benzene | 0.040% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.030% |
| Mercury | 0.002% |
| City | Population | Air Quality Index | National Avg. |
| Junction City, OH | 800 | 25 | 50.0% |
| Somerset, OH | 1,796 | 25 | 50.0% |
| New Lexington, OH | 4,707 | 25 | 50.0% |
| Fultonham, OH | 181 | 25 | 50.0% |
| Bremen, OH | 1,477 | 25 | 50.0% |
| Thornville, OH | 1,523 | 46 | 8.0% |
| City | Population | Air Quality Index | National Avg. |
| Ballplay, AL | 1,522 | 43 | 14.0% |
| Kirkland, IL | 1,524 | 42 | 16.0% |
| Hartington, NE | 1,522 | 35 | 30.0% |
| Twin Lakes, VA | 1,522 | 40 | 20.0% |
| Parsons, WV | 1,524 | 31 | 38.0% |
| Thornville, OH | 1,523 | 46 | 8.0% |
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