| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 8°F | 24°F | 16°F | 1.1" |
| February | 10°F | 28°F | 18°F | 2.5" |
| March | 25°F | 42°F | 33°F | 3.5" |
| April | 37°F | 58°F | 47°F | 4.5" |
| May | 48°F | 71°F | 59°F | 7.9" |
| June | 59°F | 80°F | 68°F | 6.7" |
| July | 63°F | 84°F | 73°F | 5.2" |
| August | 60°F | 81°F | 70°F | 6.5" |
| September | 53°F | 74°F | 62°F | 4.2" |
| October | 40°F | 60°F | 49°F | 4.5" |
| November | 27°F | 45°F | 35°F | 3.2" |
| December | 13°F | 28°F | 20°F | 2.0" |
| Index | Henderson | Minnesota | National |
| Air quality index | 46 | 35 | 42 |
| Pollution index | 848,330 | 1,854,519 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 214 |
| Days with moderate air quality | 148 |
| Days w/ poor A.Q. for sensitive groups | 2 |
| Days with unhealthy air quality | 1 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.003% |
| Mercury | 0.001% |
| City | Population | Air Quality Index | National Avg. |
| Arlington, MN | 2,451 | 46 | 8.0% |
| Le Sueur, MN | 4,028 | 46 | 8.0% |
| Heidelberg, MN | 216 | 46 | 8.0% |
| Gaylord, MN | 1,958 | 46 | 8.0% |
| Belle Plaine, MN | 7,137 | 46 | 8.0% |
| Henderson, MN | 926 | 46 | 8.0% |
| City | Population | Air Quality Index | National Avg. |
| Sweet Home, AR | 926 | 45 | 10.0% |
| Diamond, MO | 926 | 37 | 26.0% |
| Franklin, NE | 926 | 19 | 62.0% |
| Tully, NY | 926 | 37 | 26.0% |
| Hauser, ID | 927 | 43 | 14.0% |
| Henderson, MN | 926 | 46 | 8.0% |
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