Lyman, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 42.4 °F (low) to 59.9 °F (high). Annual precipitation averages 46.7 Inches. 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 | 34.0 °F | 44.8 °F | 5.93 in. |
| February | 34.2 °F | 47.8 °F | 3.81 in. |
| March | 36.7 °F | 52.5 °F | 4.87 in. |
| April | 40.4 °F | 59.2 °F | 3.58 in. |
| May | 45.6 °F | 65.9 °F | 3.02 in. |
| June | 49.8 °F | 69.7 °F | 2.29 in. |
| July | 52.3 °F | 76.1 °F | 1.2 in. |
| August | 52.3 °F | 77.0 °F | 1.31 in. |
| September | 48.6 °F | 71.6 °F | 2.42 in. |
| October | 42.7 °F | 60.5 °F | 4.92 in. |
| November | 37.8 °F | 49.9 °F | 7.73 in. |
| December | 33.9 °F | 44.1 °F | 5.62 in. |
| Annual | 42.4 °F | 59.9 °F | 46.7 in. |
| 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 : 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 |