| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 13°F | 29°F | 20°F | 0.9" |
| February | 18°F | 35°F | 25°F | 2.3" |
| March | 31°F | 56°F | 41°F | 4.5" |
| April | 40°F | 65°F | 51°F | 7.4" |
| May | 53°F | 77°F | 64°F | 9.7" |
| June | 63°F | 85°F | 73°F | 4.3" |
| July | 65°F | 89°F | 77°F | 4.2" |
| August | 64°F | 85°F | 74°F | 5.9" |
| September | 54°F | 82°F | 67°F | 2.4" |
| October | 42°F | 68°F | 54°F | 2.7" |
| November | 27°F | 53°F | 39°F | 2.5" |
| December | 12°F | 30°F | 21°F | 1.9" |
| Index | Onawa | Iowa | National |
| Air quality index | 35 | 39 | 42 |
| Pollution index | 565,451 | 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 | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Smithland, IA | 168 | 35 | 30.0% |
| Decatur, NE | 402 | 35 | 30.0% |
| Hornick, IA | 286 | 35 | 30.0% |
| Macy, NE | 927 | 35 | 30.0% |
| Blencoe, IA | 238 | 35 | 30.0% |
| Onawa, IA | 2,788 | 35 | 30.0% |
| City | Population | Air Quality Index | National Avg. |
| Lake Heritage, PA | 2,788 | 42 | 16.0% |
| Sainte-Anne-de-Beaupré, QC | 2,788 | n/a | |
| Saint-Chrysostome, QC | 2,788 | n/a | |
| Bayview, CA | 2,787 | 27 | 46.0% |
| Lake Helen, FL | 2,787 | 37 | 26.0% |
| Onawa, IA | 2,788 | 35 | 30.0% |
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