Mount Vernon, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 42.9 °F (low) to 59 °F (high). Annual precipitation averages 34.4 Inches. 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 | 35.0 °F | 46.3 °F | 4.31 in. |
| February | 34.9 °F | 48.5 °F | 3.06 in. |
| March | 37.5 °F | 52.5 °F | 3.22 in. |
| April | 40.9 °F | 57.4 °F | 2.93 in. |
| May | 45.8 °F | 63.7 °F | 2.58 in. |
| June | 50.0 °F | 67.9 °F | 1.94 in. |
| July | 52.7 °F | 73.4 °F | 0.96 in. |
| August | 52.6 °F | 74.3 °F | 1.13 in. |
| September | 49.0 °F | 68.8 °F | 1.93 in. |
| October | 43.2 °F | 59.2 °F | 3.43 in. |
| November | 38.3 °F | 50.9 °F | 4.9 in. |
| December | 34.6 °F | 45.3 °F | 3.99 in. |
| Annual | 42.9 °F | 59 °F | 34.38 in. |
| 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 : 15°F to 20°F |
| Plant Hardiness Zone - 2012 | Zone 8a : 10°F to 15°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |