| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 24°F | 43°F | 32°F | 2.5" |
| February | 26°F | 45°F | 34°F | 2.5" |
| March | 36°F | 58°F | 45°F | 4.3" |
| April | 46°F | 69°F | 57°F | 7.2" |
| May | 55°F | 76°F | 65°F | 6.3" |
| June | 64°F | 87°F | 75°F | 5.5" |
| July | 66°F | 90°F | 77°F | 10.4" |
| August | 63°F | 87°F | 75°F | 6.8" |
| September | 58°F | 85°F | 71°F | 6.4" |
| October | 49°F | 72°F | 59°F | 7.2" |
| November | 36°F | 57°F | 45°F | 7.9" |
| December | 29°F | 45°F | 36°F | 7.3" |
| Index | Gilliam | Missouri | National |
| Air quality index | 38 | 97 | 42 |
| Pollution index | 2,921,360 | 1,630,255 | 2,726,193 |
| Measurement | Total |
| Days measured | 245 |
| Days with good air quality | 239 |
| Days with moderate air quality | 6 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.002% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.070% |
| Mercury | 0.003% |
| City | Population | Air Quality Index | National Avg. |
| Keytesville, MO | 328 | 38 | 24.0% |
| Marshall, MO | 12,920 | 38 | 24.0% |
| Brunswick, MO | 972 | 38 | 24.0% |
| Salisbury, MO | 1,584 | 38 | 24.0% |
| Glasgow, MO | 1,117 | 38 | 24.0% |
| Gilliam, MO | 188 | 38 | 24.0% |
| City | Population | Air Quality Index | National Avg. |
| Adak, AK | 188 | 31 | 38.0% |
| Halibut Cove, AK | 188 | 31 | 38.0% |
| Nikolaevsk, AK | 188 | 31 | 38.0% |
| Bluff City, AR | 188 | 32 | 36.0% |
| Pinion Pines, AZ | 188 | 13 | 74.0% |
| Gilliam, MO | 188 | 38 | 24.0% |
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