Ontario, Wisconsin has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 1.4 °C (low) to 13.1 °C (high). Annual precipitation averages 956.6 Millimeters. Ontario is located in USDA Plant Hardiness Zone 4b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -13.8 °C | -3.6 °C | 31.24 mm |
| February | -12.1 °C | -0.9 °C | 28.96 mm |
| March | -5.7 °C | 5.8 °C | 48.77 mm |
| April | 0.8 °C | 13.4 °C | 96.77 mm |
| May | 7.3 °C | 20.1 °C | 115.82 mm |
| June | 13 °C | 25.3 °C | 130.81 mm |
| July | 15.1 °C | 27.4 °C | 117.09 mm |
| August | 13.8 °C | 26.3 °C | 121.16 mm |
| September | 9.1 °C | 22.3 °C | 101.85 mm |
| October | 2.5 °C | 15.1 °C | 73.15 mm |
| November | -3.6 °C | 6.6 °C | 51.56 mm |
| December | -9.8 °C | -0.6 °C | 39.37 mm |
| Annual | 1.4 °C | 13.1 °C | 956.55 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 4b : -31.7°C to -28.9°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |