Janesville, California has a Humid Continental Climate - Dry Cool Summer climate (Köppen classification: Dsb). Average annual temperatures range from 1.5 °C (low) to 18.1 °C (high). Annual precipitation averages 431.5 Millimeters. Janesville is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -5.2 °C | 6.5 °C | 83.82 mm |
| February | -4.1 °C | 8.8 °C | 66.8 mm |
| March | -1.7 °C | 12.4 °C | 53.09 mm |
| April | 0.2 °C | 15.8 °C | 23.11 mm |
| May | 3.7 °C | 20.9 °C | 25.65 mm |
| June | 7.1 °C | 26.6 °C | 16.51 mm |
| July | 10.4 °C | 31.7 °C | 6.6 mm |
| August | 9.3 °C | 31.1 °C | 4.57 mm |
| September | 5.7 °C | 27.1 °C | 6.6 mm |
| October | 1.2 °C | 19.5 °C | 26.92 mm |
| November | -2.8 °C | 11.3 °C | 36.07 mm |
| December | -5.6 °C | 5.9 °C | 81.79 mm |
| Annual | 1.5 °C | 18.1 °C | 431.53 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 7a : -17.8°C to -15°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dsb - Humid Continental Climate - Dry Cool Summer |