Lewisville, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 5.6 °C (low) to 16.4 °C (high). Annual precipitation averages 1398.8 Millimeters. Lewisville is located in USDA Plant Hardiness Zone 8b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 0.9 °C | 7.6 °C | 193.04 mm |
| February | 0.9 °C | 9.8 °C | 140.72 mm |
| March | 2.4 °C | 12.4 °C | 152.4 mm |
| April | 4.2 °C | 15.3 °C | 120.14 mm |
| May | 7.3 °C | 19.3 °C | 89.41 mm |
| June | 9.6 °C | 21.7 °C | 62.23 mm |
| July | 11.7 °C | 25.8 °C | 17.02 mm |
| August | 11.6 °C | 26.6 °C | 20.83 mm |
| September | 9.2 °C | 23.6 °C | 58.67 mm |
| October | 5.8 °C | 17.1 °C | 129.79 mm |
| November | 2.9 °C | 10.9 °C | 201.17 mm |
| December | 0.8 °C | 7.2 °C | 213.36 mm |
| Annual | 5.6 °C | 16.4 °C | 1398.78 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 50-75 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 | Abnormally Dry |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |