| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 12°F | 30°F | 21°F | 0.8" |
| February | 14°F | 34°F | 23°F | 1.0" |
| March | 28°F | 49°F | 37°F | 2.2" |
| April | 39°F | 63°F | 49°F | 4.1" |
| May | 49°F | 73°F | 60°F | 5.2" |
| June | 60°F | 83°F | 71°F | 7.1" |
| July | 64°F | 86°F | 75°F | 4.2" |
| August | 62°F | 83°F | 71°F | 5.5" |
| September | 53°F | 77°F | 63°F | 2.8" |
| October | 41°F | 64°F | 51°F | 4.0" |
| November | 28°F | 49°F | 38°F | 3.7" |
| December | 16°F | 33°F | 24°F | 2.5" |
| Index | Alton | Iowa | National |
| Air quality index | 35 | 39 | 42 |
| Pollution index | 890,079 | 1,154,535 | 2,726,193 |
| Measurement | Total |
| Days measured | 364 |
| Days with good air quality | 322 |
| Days with moderate air quality | 42 |
| 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 | 0.004% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Maurice, IA | 295 | 35 | 30.0% |
| Struble, IA | 95 | 35 | 30.0% |
| Brunsville, IA | 140 | 35 | 30.0% |
| Orange City, IA | 6,158 | 35 | 30.0% |
| Archer, IA | 116 | 35 | 30.0% |
| Alton, IA | 1,534 | 35 | 30.0% |
| City | Population | Air Quality Index | National Avg. |
| London, CA | 1,534 | 66 | 32.0% |
| Wolcott, NY | 1,534 | 37 | 26.0% |
| Falling Water, TN | 1,534 | 46 | 8.0% |
| Hughes Springs, TX | 1,534 | 37 | 26.0% |
| Upper Island Cove, NL | 1,534 | n/a | |
| Alton, IA | 1,534 | 35 | 30.0% |
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