Mount Vernon, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 6 °C (low) to 15 °C (high). Annual precipitation averages 873.2 Millimeters. Mount Vernon is located in USDA Plant Hardiness Zone 8b. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Nov. 1 - Nov. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 1.7 °C | 7.9 °C | 109.47 mm |
| February | 1.6 °C | 9.2 °C | 77.72 mm |
| March | 3.1 °C | 11.4 °C | 81.79 mm |
| April | 4.9 °C | 14.1 °C | 74.42 mm |
| May | 7.7 °C | 17.6 °C | 65.53 mm |
| June | 10 °C | 19.9 °C | 49.28 mm |
| July | 11.5 °C | 23 °C | 24.38 mm |
| August | 11.4 °C | 23.5 °C | 28.7 mm |
| September | 9.4 °C | 20.4 °C | 49.02 mm |
| October | 6.2 °C | 15.1 °C | 87.12 mm |
| November | 3.5 °C | 10.5 °C | 124.46 mm |
| December | 1.4 °C | 7.4 °C | 101.35 mm |
| Annual | 6 °C | 15 °C | 873.24 mm |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 40-50 Days |
| Plant Hardiness Zone | Zone 8b : -9.4°C to -6.7°C |
| Plant Hardiness Zone - 2012 | Zone 8a : -12.2°C to -9.4°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |