| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 11°F | 28°F | 19°F | 0.9" |
| February | 13°F | 31°F | 21°F | 2.2" |
| March | 28°F | 47°F | 36°F | 3.6" |
| April | 39°F | 62°F | 49°F | 6.9" |
| May | 50°F | 73°F | 60°F | 6.0" |
| June | 60°F | 82°F | 70°F | 6.7" |
| July | 64°F | 85°F | 74°F | 7.7" |
| August | 61°F | 82°F | 71°F | 11.0" |
| September | 53°F | 76°F | 64°F | 5.6" |
| October | 41°F | 63°F | 51°F | 5.4" |
| November | 29°F | 48°F | 38°F | 2.4" |
| December | 16°F | 32°F | 23°F | 2.9" |
| Index | Barnum | Iowa | National |
| Air quality index | 37 | 39 | 42 |
| Pollution index | 517,691 | 1,154,535 | 2,726,193 |
| Measurement | Total |
| Days measured | 214 |
| Days with good air quality | 210 |
| Days with moderate air quality | 4 |
| Days w/ poor A.Q. for sensitive groups | |
| Days with unhealthy air quality |
| 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. |
| Humboldt, IA | 4,568 | 37 | 26.0% |
| Coalville, IA | 645 | 37 | 26.0% |
| Otho, IA | 479 | 37 | 26.0% |
| Rockwell City, IA | 2,166 | 37 | 26.0% |
| Badger, IA | 448 | 37 | 26.0% |
| Barnum, IA | 323 | 37 | 26.0% |
| City | Population | Air Quality Index | National Avg. |
| Manalapan, FL | 323 | 36 | 28.0% |
| Medora, IL | 323 | 54 | 8.0% |
| Stinesville, IN | 323 | 42 | 16.0% |
| Montpelier, LA | 323 | 30 | 40.0% |
| East New Market, MD | 323 | 41 | 18.0% |
| Barnum, IA | 323 | 37 | 26.0% |
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