| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 23°F | 39°F | 29°F | 4.4" |
| February | 27°F | 45°F | 34°F | 4.9" |
| March | 39°F | 61°F | 48°F | 5.2" |
| April | 45°F | 65°F | 55°F | 4.7" |
| May | 57°F | 77°F | 66°F | 8.9" |
| June | 66°F | 83°F | 74°F | 15.3" |
| July | 69°F | 88°F | 78°F | 9.5" |
| August | 71°F | 89°F | 79°F | 10.9" |
| September | 62°F | 82°F | 71°F | 4.7" |
| October | 50°F | 69°F | 58°F | 8.9" |
| November | 37°F | 57°F | 46°F | 4.0" |
| December | 23°F | 40°F | 30°F | 3.3" |
| Index | Merwin | Missouri | National |
| Air quality index | 47 | 97 | 42 |
| Pollution index | 8,275,060 | 1,630,255 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 210 |
| Days with moderate air quality | 154 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.300% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.080% |
| Mercury | 0.190% |
| City | Population | Air Quality Index | National Avg. |
| Amoret, MO | 153 | 47 | 6.0% |
| Linn Valley, KS | 861 | 47 | 6.0% |
| Adrian, MO | 2,058 | 47 | 6.0% |
| Butler, MO | 4,125 | 47 | 6.0% |
| Louisburg, KS | 4,499 | 47 | 6.0% |
| Merwin, MO | 57 | 47 | 6.0% |
| City | Population | Air Quality Index | National Avg. |
| Crooked Creek, AK | 57 | 31 | 38.0% |
| Crown Point, AK | 57 | 31 | 38.0% |
| Pelican, AK | 57 | 20 | 60.0% |
| Carlton, AL | 57 | 42 | 16.0% |
| Amagon, AR | 57 | 45 | 10.0% |
| Merwin, MO | 57 | 47 | 6.0% |
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