Ontario, Oregon has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 4 °C (low) to 18.3 °C (high). Annual precipitation averages 239.5 Millimeters. Ontario is located in USDA Plant Hardiness Zone 7a. 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 | -5 °C | 2.8 °C | 27.18 mm |
| February | -3.1 °C | 7.7 °C | 19.3 mm |
| March | 0.1 °C | 13.9 °C | 21.34 mm |
| April | 2.9 °C | 18.1 °C | 20.83 mm |
| May | 7.8 °C | 23.3 °C | 30.99 mm |
| June | 11.6 °C | 27.9 °C | 17.27 mm |
| July | 15.4 °C | 33.8 °C | 7.87 mm |
| August | 13.9 °C | 33.1 °C | 2.79 mm |
| September | 8.8 °C | 27.2 °C | 9.14 mm |
| October | 2.8 °C | 18.9 °C | 18.03 mm |
| November | -1.9 °C | 9.7 °C | 25.15 mm |
| December | -4.9 °C | 3.4 °C | 39.62 mm |
| Annual | 4 °C | 18.3 °C | 239.51 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |