Ontario, Wisconsin has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 34.5 °F (low) to 55.6 °F (high). Annual precipitation averages 37.7 Inches. 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 | 7.2 °F | 25.6 °F | 1.23 in. |
| February | 10.3 °F | 30.4 °F | 1.14 in. |
| March | 21.7 °F | 42.4 °F | 1.92 in. |
| April | 33.4 °F | 56.2 °F | 3.81 in. |
| May | 45.1 °F | 68.2 °F | 4.56 in. |
| June | 55.4 °F | 77.5 °F | 5.15 in. |
| July | 59.2 °F | 81.3 °F | 4.61 in. |
| August | 56.9 °F | 79.4 °F | 4.77 in. |
| September | 48.3 °F | 72.1 °F | 4.01 in. |
| October | 36.5 °F | 59.1 °F | 2.88 in. |
| November | 25.5 °F | 43.8 °F | 2.03 in. |
| December | 14.4 °F | 31.0 °F | 1.55 in. |
| Annual | 34.5 °F | 55.6 °F | 37.66 in. |
| 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 : -25°F to -20°F |
| Plant Hardiness Zone - 2012 | Zone 4b : -25°F to -20°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |