| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 12°F | 27°F | 19°F | 0.7" |
| February | 13°F | 29°F | 21°F | 0.7" |
| March | 29°F | 45°F | 36°F | 1.7" |
| April | 39°F | 60°F | 48°F | 2.8" |
| May | 50°F | 71°F | 60°F | 2.4" |
| June | 60°F | 80°F | 70°F | 5.1" |
| July | 62°F | 82°F | 72°F | 2.5" |
| August | 60°F | 79°F | 69°F | 2.3" |
| September | 53°F | 75°F | 63°F | 3.0" |
| October | 42°F | 61°F | 50°F | 2.8" |
| November | 29°F | 47°F | 37°F | 1.1" |
| December | 17°F | 31°F | 24°F | 1.8" |
| Index | Winthrop | Iowa | National |
| Air quality index | 39 | 39 | 42 |
| Pollution index | 586,175 | 1,154,535 | 2,726,193 |
| Measurement | Total |
| Days measured | 363 |
| Days with good air quality | 286 |
| Days with moderate air quality | 77 |
| 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 | 0.090% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Lamont, IA | 519 | 39 | 22.0% |
| Ryan, IA | 340 | 39 | 22.0% |
| Manchester, IA | 5,011 | 39 | 22.0% |
| Oelwein, IA | 5,896 | 39 | 22.0% |
| Aurora, IA | 175 | 39 | 22.0% |
| Winthrop, IA | 1,025 | 39 | 22.0% |
| City | Population | Air Quality Index | National Avg. |
| Salamatof, AK | 1,025 | 31 | 38.0% |
| Santa Margarita, CA | 1,025 | 46 | 8.0% |
| West Park, CA | 1,025 | 60 | 20.0% |
| Montgomery, IN | 1,025 | 1 | 98.0% |
| Brush Fork, WV | 1,025 | 295 | 490.0% |
| Winthrop, IA | 1,025 | 39 | 22.0% |
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