| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 25°F | 41°F | 32°F | 5.0" |
| February | 26°F | 43°F | 34°F | 3.4" |
| March | 38°F | 58°F | 47°F | 4.9" |
| April | 47°F | 69°F | 57°F | 9.7" |
| May | 57°F | 77°F | 66°F | 7.4" |
| June | 66°F | 87°F | 76°F | 8.6" |
| July | 68°F | 89°F | 78°F | 6.6" |
| August | 66°F | 88°F | 76°F | 8.7" |
| September | 58°F | 81°F | 68°F | 7.6" |
| October | 47°F | 70°F | 58°F | 7.1" |
| November | 37°F | 57°F | 46°F | 6.0" |
| December | 30°F | 45°F | 36°F | 6.6" |
| Index | Centralia | Illinois | National |
| Air quality index | 43 | 41 | 42 |
| Pollution index | 647,280 | 3,148,694 | 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 | 0.020% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Ashley, IL | 471 | 43 | 14.0% |
| Mount Vernon, IL | 14,769 | 43 | 14.0% |
| Odin, IL | 999 | 43 | 14.0% |
| Hoffman, IL | 775 | 43 | 14.0% |
| Wamac, IL | 1,222 | 43 | 14.0% |
| Centralia, IL | 12,354 | 43 | 14.0% |
| City | Population | Air Quality Index | National Avg. |
| Wellesley, ON | 12,358 | n/a | |
| Grenada, MS | 12,349 | 33 | 34.0% |
| Winnetka, IL | 12,361 | 55 | 10.0% |
| Lakeland Village, CA | 12,362 | 89 | 78.0% |
| Urbana, MD | 12,362 | 40 | 20.0% |
| Centralia, IL | 12,354 | 43 | 14.0% |
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