Vernonia, Oregon has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 4.2 °C (low) to 16.1 °C (high). Annual precipitation averages 1242.6 Millimeters. Vernonia is located in USDA Plant Hardiness Zone 8a. 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 | -0.2 °C | 7.7 °C | 186.69 mm |
| February | -0.3 °C | 9.7 °C | 136.91 mm |
| March | 1.1 °C | 12.2 °C | 136.91 mm |
| April | 2.7 °C | 14.7 °C | 100.33 mm |
| May | 5.7 °C | 18.6 °C | 62.48 mm |
| June | 8.1 °C | 21.3 °C | 38.35 mm |
| July | 10.2 °C | 25.3 °C | 10.41 mm |
| August | 10.1 °C | 25.9 °C | 14.73 mm |
| September | 7.6 °C | 23 °C | 42.67 mm |
| October | 4.2 °C | 16.7 °C | 106.93 mm |
| November | 1.7 °C | 10.7 °C | 192.28 mm |
| December | -0.3 °C | 7.1 °C | 213.87 mm |
| Annual | 4.2 °C | 16.1 °C | 1242.56 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 8a : -12.2°C to -9.4°C |
| Plant Hardiness Zone - 2012 | Zone 8a : -12.2°C to -9.4°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |