| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 15°F | 28°F | 21°F | 1.8" |
| February | 15°F | 30°F | 22°F | 1.1" |
| March | 26°F | 43°F | 34°F | 3.6" |
| April | 36°F | 56°F | 45°F | 7.5" |
| May | 47°F | 68°F | 56°F | 4.1" |
| June | 56°F | 77°F | 66°F | 4.1" |
| July | 60°F | 81°F | 70°F | 1.5" |
| August | 59°F | 78°F | 68°F | 4.1" |
| September | 51°F | 72°F | 61°F | 5.1" |
| October | 42°F | 59°F | 50°F | 5.8" |
| November | 31°F | 46°F | 38°F | 2.1" |
| December | 20°F | 32°F | 26°F | 4.5" |
| Index | Grafton | Wisconsin | National |
| Air quality index | 44 | 69 | 42 |
| Pollution index | 3,171,080 | 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 | 0.010% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.003% |
| Lead | 0.010% |
| Mercury | 0.100% |
| City | Population | Air Quality Index | National Avg. |
| Kewaskum, WI | 4,224 | 36 | 28.0% |
| Belgium, WI | 2,201 | 38 | 24.0% |
| Fredonia, WI | 2,466 | 38 | 24.0% |
| Waubeka, WI | 624 | 38 | 24.0% |
| Butler, WI | 1,964 | 44 | 12.0% |
| Grafton, WI | 11,718 | 44 | 12.0% |
| City | Population | Air Quality Index | National Avg. |
| Webster, MA | 11,719 | 40 | 20.0% |
| Florham Park, NJ | 11,719 | 51 | 2.0% |
| Wanaque, NJ | 11,719 | 51 | 2.0% |
| Stratford, PE | 11,716 | n/a | |
| Arlington, TN | 11,715 | 45 | 10.0% |
| Grafton, WI | 11,718 | 44 | 12.0% |
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