| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 25°F | 41°F | 33°F | 8.9" |
| February | 20°F | 38°F | 29°F | 4.8" |
| March | 34°F | 56°F | 44°F | 3.7" |
| April | 41°F | 66°F | 53°F | 7.5" |
| May | 52°F | 77°F | 65°F | 5.1" |
| June | 62°F | 86°F | 74°F | 8.7" |
| July | 63°F | 86°F | 74°F | 9.6" |
| August | 66°F | 88°F | 76°F | 6.0" |
| September | 57°F | 83°F | 69°F | 12.3" |
| October | 48°F | 70°F | 58°F | 6.4" |
| November | 33°F | 56°F | 44°F | 6.5" |
| December | 25°F | 39°F | 31°F | 3.6" |
| Index | Riley | Indiana | National |
| Air quality index | 45 | 56 | 42 |
| Pollution index | 1,601,640 | 2,719,453 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 237 |
| Days with moderate air quality | 127 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.004% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.040% |
| Mercury | 0.290% |
| City | Population | Air Quality Index | National Avg. |
| Terre Haute, IN | 60,690 | 45 | 10.0% |
| Fontanet, IN | 468 | 45 | 10.0% |
| Tecumseh, IN | 778 | 45 | 10.0% |
| St. Mary of the Woods, IN | 819 | 45 | 10.0% |
| Clay City, IN | 1,273 | 45 | 10.0% |
| Riley, IN | 453 | 45 | 10.0% |
| City | Population | Air Quality Index | National Avg. |
| Boulevard, CA | 453 | 58 | 16.0% |
| Argyle, GA | 453 | 26 | 48.0% |
| Martin, GA | 453 | 41 | 18.0% |
| Allerton, IA | 453 | 39 | 22.0% |
| Essex, MO | 453 | 26 | 48.0% |
| Riley, IN | 453 | 45 | 10.0% |
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