| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 15°F | 28°F | 21°F | 0.6" |
| February | 15°F | 29°F | 22°F | 2.8" |
| March | 27°F | 43°F | 34°F | 2.9" |
| April | 37°F | 55°F | 45°F | 3.1" |
| May | 47°F | 67°F | 56°F | 8.9" |
| June | 56°F | 76°F | 66°F | 19.6" |
| July | 61°F | 80°F | 70°F | 14.9" |
| August | 60°F | 78°F | 69°F | 2.3" |
| September | 53°F | 72°F | 61°F | 10.4" |
| October | 42°F | 59°F | 50°F | 6.6" |
| November | 31°F | 46°F | 38°F | 3.6" |
| December | 20°F | 32°F | 26°F | 1.8" |
| Index | Hartland | Wisconsin | National |
| Air quality index | 44 | 69 | 42 |
| Pollution index | 17,168,000 | 2,842,418 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 254 |
| Days with moderate air quality | 108 |
| Days w/ poor A.Q. for sensitive groups | 3 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.030% |
| Benzene | 0.160% |
| Carbon Tetrachloride | 0.050% |
| Lead | 0.160% |
| Mercury | 0.150% |
| City | Population | Air Quality Index | National Avg. |
| Nashotah, WI | 1,287 | 37 | 26.0% |
| Oconomowoc Lake, WI | 621 | 37 | 26.0% |
| Ixonia, WI | 1,856 | 37 | 26.0% |
| North Prairie, WI | 2,542 | 37 | 26.0% |
| Okauchee Lake, WI | 4,373 | 37 | 26.0% |
| Hartland, WI | 9,317 | 44 | 12.0% |
| City | Population | Air Quality Index | National Avg. |
| Eagle Point, OR | 9,316 | 36 | 28.0% |
| Flossmoor, IL | 9,318 | 55 | 10.0% |
| Brentwood, PA | 9,319 | 56 | 12.0% |
| Leisure World, MD | 9,314 | 47 | 6.0% |
| Sellersburg, IN | 9,320 | 49 | 2.0% |
| Hartland, WI | 9,317 | 44 | 12.0% |
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