Lyman, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 5.8 °C (low) to 15.5 °C (high). Annual precipitation averages 1186.2 Millimeters. Lyman 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 | 1.1 °C | 7.1 °C | 150.62 mm |
| February | 1.2 °C | 8.8 °C | 96.77 mm |
| March | 2.6 °C | 11.4 °C | 123.7 mm |
| April | 4.7 °C | 15.1 °C | 90.93 mm |
| May | 7.6 °C | 18.8 °C | 76.71 mm |
| June | 9.9 °C | 20.9 °C | 58.17 mm |
| July | 11.3 °C | 24.5 °C | 30.48 mm |
| August | 11.3 °C | 25 °C | 33.27 mm |
| September | 9.2 °C | 22 °C | 61.47 mm |
| October | 5.9 °C | 15.8 °C | 124.97 mm |
| November | 3.2 °C | 9.9 °C | 196.34 mm |
| December | 1.1 °C | 6.7 °C | 142.75 mm |
| Annual | 5.8 °C | 15.5 °C | 1186.18 mm |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| 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 | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |