| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 26°F | 43°F | 34°F | 2.0" |
| February | 28°F | 46°F | 36°F | 2.7" |
| March | 38°F | 59°F | 47°F | 3.6" |
| April | 48°F | 71°F | 58°F | 6.1" |
| May | 57°F | 78°F | 67°F | 4.7" |
| June | 66°F | 88°F | 76°F | 3.8" |
| July | 67°F | 88°F | 76°F | 5.7" |
| August | 65°F | 87°F | 75°F | 2.8" |
| September | 57°F | 82°F | 68°F | 3.2" |
| October | 46°F | 71°F | 57°F | 4.2" |
| November | 36°F | 57°F | 46°F | 4.1" |
| December | 30°F | 46°F | 37°F | 2.7" |
| Index | Grayville | Illinois | National |
| Air quality index | 45 | 41 | 42 |
| Pollution index | 317,387 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 244 |
| Days with moderate air quality | 111 |
| Days w/ poor A.Q. for sensitive groups | 10 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Bellmont, IL | 238 | 36 | 28.0% |
| Bone Gap, IL | 151 | 36 | 28.0% |
| Keensburg, IL | 111 | 36 | 28.0% |
| Browns, IL | 226 | 36 | 28.0% |
| Mount Carmel, IL | 6,922 | 36 | 28.0% |
| Grayville, IL | 1,579 | 45 | 10.0% |
| City | Population | Air Quality Index | National Avg. |
| Neoga, IL | 1,579 | 40 | 20.0% |
| Towanda, KS | 1,579 | 40 | 20.0% |
| Leadwood, MO | 1,579 | 54 | 8.0% |
| Alum Creek, WV | 1,579 | 40 | 20.0% |
| Sainte-Anne-de-la-Pocatière, QC | 1,579 | n/a | |
| Grayville, IL | 1,579 | 45 | 10.0% |
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