| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 27°F | 47°F | 36°F | 2.6" |
| February | 30°F | 50°F | 39°F | 10.5" |
| March | 41°F | 62°F | 50°F | 6.8" |
| April | 50°F | 71°F | 60°F | 5.0" |
| May | 58°F | 77°F | 67°F | 7.5" |
| June | 69°F | 88°F | 78°F | 11.1" |
| July | 72°F | 92°F | 81°F | 4.9" |
| August | 70°F | 92°F | 80°F | 10.2" |
| September | 62°F | 83°F | 71°F | 16.4" |
| October | 50°F | 72°F | 60°F | 4.3" |
| November | 40°F | 60°F | 48°F | 5.8" |
| December | 31°F | 48°F | 39°F | 2.5" |
| Index | Irwin | Missouri | National |
| Air quality index | 37 | 97 | 42 |
| Pollution index | 1,317,960 | 1,630,255 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 324 |
| Days with moderate air quality | 40 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.002% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Moundville, MO | 106 | 37 | 26.0% |
| Lamar Heights, MO | 149 | 37 | 26.0% |
| Golden City, MO | 639 | 37 | 26.0% |
| Milford, MO | 3 | 37 | 26.0% |
| Bronaugh, MO | 193 | 37 | 26.0% |
| Irwin, MO | 22 | 37 | 26.0% |
| City | Population | Air Quality Index | National Avg. |
| Dot Lake Village, AK | 22 | 38 | 24.0% |
| Coppock, IA | 22 | 35 | 30.0% |
| Pioneer, IA | 22 | 37 | 26.0% |
| Byers, KS | 22 | 15 | 70.0% |
| Lupus, MO | 22 | 38 | 24.0% |
| Irwin, MO | 22 | 37 | 26.0% |
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