| 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 | Denison | Iowa | National |
| Air quality index | 35 | 39 | 42 |
| Pollution index | 517,691 | 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. |
| Kiron, IA | 321 | 35 | 30.0% |
| Westside, IA | 248 | 35 | 30.0% |
| Charter Oak, IA | 570 | 35 | 30.0% |
| Schleswig, IA | 979 | 35 | 30.0% |
| Ricketts, IA | 92 | 35 | 30.0% |
| Denison, IA | 8,319 | 35 | 30.0% |
| City | Population | Air Quality Index | National Avg. |
| Long Hill, CT | 8,315 | 37 | 26.0% |
| Athol, MA | 8,323 | 34 | 32.0% |
| Roxboro, NC | 8,323 | 44 | 12.0% |
| Hawthorn Woods, IL | 8,313 | 55 | 10.0% |
| Baxter, MN | 8,326 | 29 | 42.0% |
| Denison, IA | 8,319 | 35 | 30.0% |
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