| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 29°F | 46°F | 36°F | 7.4" |
| February | 29°F | 50°F | 38°F | 6.4" |
| March | 40°F | 63°F | 51°F | 2.9" |
| April | 46°F | 67°F | 56°F | 7.0" |
| May | 55°F | 78°F | 67°F | 4.1" |
| June | 63°F | 86°F | 74°F | 4.4" |
| July | 66°F | 88°F | 77°F | 10.3" |
| August | 69°F | 93°F | 80°F | 7.0" |
| September | 62°F | 84°F | 72°F | 10.2" |
| October | 50°F | 71°F | 59°F | 4.8" |
| November | 38°F | 60°F | 48°F | 9.4" |
| December | 28°F | 46°F | 36°F | 5.9" |
| Index | Alton | Missouri | National |
| Air quality index | 36 | 97 | 42 |
| Pollution index | 305,376 | 1,630,255 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 347 |
| 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. |
| Thayer, MO | 2,578 | 36 | 28.0% |
| Thomasville, MO | 0 | 36 | 28.0% |
| Mammoth Spring, AR | 1,117 | 36 | 28.0% |
| Koshkonong, MO | 153 | 36 | 28.0% |
| Alton, MO | 638 | 36 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| Mountain Park city, GA | 638 | 52 | 4.0% |
| Elgin, IA | 638 | 39 | 22.0% |
| Oretta, LA | 638 | 45 | 10.0% |
| Lake Benton, MN | 638 | 42 | 16.0% |
| Warner, NH | 638 | 27 | 46.0% |
| Alton, MO | 638 | 36 | 28.0% |
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