| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 13°F | 29°F | 20°F | 0.2" |
| February | 14°F | 31°F | 22°F | 2.0" |
| March | 29°F | 47°F | 36°F | 0.7" |
| April | 39°F | 61°F | 49°F | 3.9" |
| May | 50°F | 73°F | 61°F | 5.8" |
| June | 61°F | 82°F | 71°F | 2.9" |
| July | 64°F | 85°F | 74°F | 2.8" |
| August | 62°F | 81°F | 70°F | 2.6" |
| September | 54°F | 76°F | 64°F | 2.7" |
| October | 42°F | 62°F | 51°F | 1.9" |
| November | 29°F | 49°F | 37°F | 0.9" |
| December | 17°F | 32°F | 24°F | 3.5" |
| Index | Marathon | Iowa | National |
| Air quality index | 35 | 39 | 42 |
| Pollution index | 769,697 | 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 | 0.001% |
| Lead | 0.002% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Ayrshire, IA | 145 | 15 | 70.0% |
| Curlew, IA | 67 | 15 | 70.0% |
| Greenville, IA | 62 | 35 | 30.0% |
| Sioux Rapids, IA | 920 | 35 | 30.0% |
| Truesdale, IA | 113 | 35 | 30.0% |
| Marathon, IA | 183 | 35 | 30.0% |
| City | Population | Air Quality Index | National Avg. |
| Litchfield, CA | 183 | 46 | 8.0% |
| Dinosaur, CO | 183 | 49 | 2.0% |
| Washta, IA | 183 | 35 | 30.0% |
| Schneider, IN | 183 | 55 | 10.0% |
| Belleview, KY | 183 | 54 | 8.0% |
| Marathon, IA | 183 | 35 | 30.0% |
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