| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 8°F | 28°F | 18°F | 1.0" |
| February | 9°F | 30°F | 20°F | 0.6" |
| March | 24°F | 46°F | 34°F | 1.5" |
| April | 34°F | 59°F | 46°F | 3.7" |
| May | 44°F | 71°F | 57°F | 4.5" |
| June | 54°F | 80°F | 67°F | 5.6" |
| July | 57°F | 84°F | 71°F | 6.2" |
| August | 56°F | 81°F | 68°F | 4.8" |
| September | 48°F | 74°F | 60°F | 5.4" |
| October | 37°F | 61°F | 48°F | 3.4" |
| November | 27°F | 46°F | 36°F | 1.5" |
| December | 14°F | 32°F | 23°F | 2.3" |
| Index | Ontario | Wisconsin | National |
| Air quality index | 35 | 69 | 42 |
| Pollution index | 2,073,170 | 2,842,418 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 310 |
| Days with moderate air quality | 55 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.030% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.010% |
| Mercury | 0.040% |
| City | Population | Air Quality Index | National Avg. |
| Cashton, WI | 961 | 35 | 30.0% |
| Norwalk, WI | 713 | 35 | 30.0% |
| Westby, WI | 2,387 | 35 | 30.0% |
| Hillsboro, WI | 1,357 | 35 | 30.0% |
| Sparta, WI | 9,751 | 35 | 30.0% |
| Ontario, WI | 477 | 35 | 30.0% |
| City | Population | Air Quality Index | National Avg. |
| Verndale, MN | 477 | 29 | 42.0% |
| Burlington Junction, MO | 477 | 43 | 14.0% |
| Oak Grove Village, MO | 477 | 54 | 8.0% |
| Morven, NC | 477 | 40 | 20.0% |
| Hildreth, NE | 477 | 19 | 62.0% |
| Ontario, WI | 477 | 35 | 30.0% |
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