Lynden, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 5.8 °C (low) to 15.1 °C (high). Annual precipitation averages 1151.6 Millimeters. Lynden is located in USDA Plant Hardiness Zone 8a. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 0.8 °C | 6.9 °C | 151.89 mm |
| February | 1.2 °C | 8.7 °C | 92.46 mm |
| March | 2.6 °C | 11.2 °C | 122.68 mm |
| April | 4.7 °C | 14.4 °C | 92.2 mm |
| May | 7.6 °C | 18.2 °C | 73.91 mm |
| June | 10.2 °C | 20.6 °C | 50.29 mm |
| July | 11.7 °C | 23.9 °C | 34.8 mm |
| August | 11.5 °C | 24.3 °C | 31.24 mm |
| September | 9 °C | 21.2 °C | 57.91 mm |
| October | 6 °C | 15.2 °C | 134.11 mm |
| November | 3.1 °C | 9.9 °C | 166.12 mm |
| December | 0.8 °C | 6.6 °C | 144.02 mm |
| Annual | 5.8 °C | 15.1 °C | 1151.63 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 50-75 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 | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |