Oconomowoc, Wisconsin has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 2.8 °C (low) to 13.5 °C (high). Annual precipitation averages 926.3 Millimeters. Oconomowoc is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.6 °C | -2.7 °C | 41.66 mm |
| February | -10.1 °C | -0.6 °C | 40.39 mm |
| March | -4.4 °C | 5.9 °C | 52.07 mm |
| April | 1.8 °C | 13.3 °C | 95.5 mm |
| May | 8.2 °C | 19.9 °C | 104.9 mm |
| June | 13.7 °C | 25.4 °C | 124.46 mm |
| July | 16.1 °C | 27.7 °C | 103.89 mm |
| August | 15.1 °C | 26.7 °C | 102.87 mm |
| September | 10.6 °C | 22.9 °C | 84.58 mm |
| October | 4.3 °C | 15.6 °C | 73.15 mm |
| November | -2 °C | 7.4 °C | 55.12 mm |
| December | -7.8 °C | 0.4 °C | 47.75 mm |
| Annual | 2.8 °C | 13.5 °C | 926.34 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |