| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 26°F | 44°F | 34°F | 5.7" |
| February | 27°F | 46°F | 36°F | 5.3" |
| March | 38°F | 59°F | 48°F | 7.5" |
| April | 47°F | 71°F | 58°F | 8.0" |
| May | 56°F | 77°F | 66°F | 8.8" |
| June | 64°F | 86°F | 74°F | 6.4" |
| July | 67°F | 87°F | 77°F | 8.3" |
| August | 66°F | 87°F | 76°F | 6.3" |
| September | 59°F | 81°F | 69°F | 8.4" |
| October | 47°F | 70°F | 58°F | 8.6" |
| November | 37°F | 58°F | 47°F | 5.9" |
| December | 30°F | 48°F | 38°F | 7.8" |
| Index | Alton | Indiana | National |
| Air quality index | 6 | 56 | 42 |
| Pollution index | 547,315 | 2,719,453 | 2,726,193 |
| Measurement | Total |
| Days measured | 272 |
| Days with good air quality | 254 |
| Days with moderate air quality | 18 |
| 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 | 0.001% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Leavenworth, IN | 406 | 6 | 88.0% |
| Brandenburg, KY | 2,874 | 39 | 22.0% |
| Ekron, KY | 266 | 39 | 22.0% |
| Mauckport, IN | 32 | 39 | 22.0% |
| New Amsterdam, IN | 103 | 49 | 2.0% |
| Alton, IN | 23 | 6 | 88.0% |
| City | Population | Air Quality Index | National Avg. |
| Ferry, AK | 23 | 38 | 24.0% |
| Benton, AL | 23 | 52 | 4.0% |
| Oak Hill, AL | 23 | 52 | 4.0% |
| Coulterville, CA | 23 | 39 | 22.0% |
| Parshall, CO | 23 | 47 | 6.0% |
| Alton, IN | 23 | 6 | 88.0% |
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