Janesville, Wisconsin has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3.3 °C (low) to 14.1 °C (high). Annual precipitation averages 946.7 Millimeters. Janesville is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.1 °C | -2.3 °C | 39.88 mm |
| February | -9.4 °C | -0.1 °C | 41.4 mm |
| March | -3.6 °C | 6.7 °C | 52.58 mm |
| April | 2.3 °C | 14.1 °C | 92.96 mm |
| May | 8.8 °C | 20.7 °C | 107.19 mm |
| June | 14.3 °C | 26.2 °C | 135.38 mm |
| July | 16.6 °C | 28.2 °C | 96.27 mm |
| August | 15.6 °C | 27.3 °C | 108.2 mm |
| September | 10.9 °C | 23.6 °C | 92.2 mm |
| October | 4.4 °C | 16.2 °C | 74.17 mm |
| November | -1.6 °C | 7.8 °C | 58.67 mm |
| December | -7.4 °C | 0.8 °C | 47.75 mm |
| Annual | 3.3 °C | 14.1 °C | 946.65 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| 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 | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |