| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 30°F | 44°F | 36°F | 7.5" |
| February | 28°F | 46°F | 36°F | 4.9" |
| March | 38°F | 61°F | 49°F | 4.2" |
| April | 45°F | 67°F | 56°F | 5.8" |
| May | 55°F | 79°F | 67°F | 4.4" |
| June | 65°F | 87°F | 76°F | 5.4" |
| July | 66°F | 87°F | 76°F | 3.6" |
| August | 69°F | 92°F | 80°F | 3.8" |
| September | 60°F | 85°F | 71°F | 5.0" |
| October | 48°F | 73°F | 59°F | 5.5" |
| November | 38°F | 59°F | 48°F | 11.1" |
| December | 28°F | 45°F | 36°F | 6.7" |
| Index | Longtown | Missouri | National |
| Air quality index | 43 | 97 | 42 |
| Pollution index | 753,473 | 1,630,255 | 2,726,193 |
| Measurement | Total |
| Days measured | 344 |
| Days with good air quality | 269 |
| Days with moderate air quality | 74 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.020% |
| Mercury | 0.020% |
| City | Population | Air Quality Index | National Avg. |
| Altenburg, MO | 345 | 43 | 14.0% |
| Frohna, MO | 319 | 43 | 14.0% |
| Rockwood, IL | 25 | 43 | 14.0% |
| Biehle, MO | 28 | 43 | 14.0% |
| Grand Tower, IL | 589 | 43 | 14.0% |
| Longtown, MO | 127 | 43 | 14.0% |
| City | Population | Air Quality Index | National Avg. |
| Goodnews Bay, AK | 127 | 31 | 38.0% |
| Delaplaine, AR | 127 | 26 | 48.0% |
| Divide, CO | 127 | 45 | 10.0% |
| Seven Hills, CO | 127 | 47 | 6.0% |
| Springbrook, IA | 127 | 42 | 16.0% |
| Longtown, MO | 127 | 43 | 14.0% |
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