Vernonia, Oregon has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 39.6 °F (low) to 60.9 °F (high). Annual precipitation averages 48.9 Inches. 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 | 31.7 °F | 45.8 °F | 7.35 in. |
| February | 31.4 °F | 49.5 °F | 5.39 in. |
| March | 34.0 °F | 53.9 °F | 5.39 in. |
| April | 36.8 °F | 58.4 °F | 3.95 in. |
| May | 42.2 °F | 65.4 °F | 2.46 in. |
| June | 46.5 °F | 70.3 °F | 1.51 in. |
| July | 50.3 °F | 77.6 °F | 0.41 in. |
| August | 50.1 °F | 78.7 °F | 0.58 in. |
| September | 45.6 °F | 73.4 °F | 1.68 in. |
| October | 39.6 °F | 62.0 °F | 4.21 in. |
| November | 35.0 °F | 51.3 °F | 7.57 in. |
| December | 31.5 °F | 44.7 °F | 8.42 in. |
| Annual | 39.6 °F | 60.9 °F | 48.92 in. |
| 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 : 10°F to 15°F |
| Plant Hardiness Zone - 2012 | Zone 8a : 10°F to 15°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |