Cornelius, Oregon has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 6.4 °C (low) to 17.3 °C (high). Annual precipitation averages 1076.2 Millimeters. Cornelius is located in USDA Plant Hardiness Zone 8b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 1.8 °C | 8.3 °C | 169.16 mm |
| February | 1.8 °C | 10.4 °C | 121.41 mm |
| March | 3.2 °C | 13.1 °C | 115.57 mm |
| April | 4.9 °C | 16.1 °C | 79.5 mm |
| May | 8 °C | 20.1 °C | 52.58 mm |
| June | 10.4 °C | 22.9 °C | 33.53 mm |
| July | 12.6 °C | 27.4 °C | 7.87 mm |
| August | 12.5 °C | 27.8 °C | 12.19 mm |
| September | 10.1 °C | 24.6 °C | 32.51 mm |
| October | 6.6 °C | 17.7 °C | 87.38 mm |
| November | 3.7 °C | 11.4 °C | 162.05 mm |
| December | 1.6 °C | 7.8 °C | 202.44 mm |
| Annual | 6.4 °C | 17.3 °C | 1076.19 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 50-75 Days |
| Plant Hardiness Zone | Zone 8b : -9.4°C to -6.7°C |
| Plant Hardiness Zone - 2012 | Zone 8b : -9.4°C to -6.7°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |