Chehalis, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 42.2 °F (low) to 62 °F (high). Annual precipitation averages 47.1 Inches. Chehalis is located in USDA Plant Hardiness Zone 8b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 35.0 °F | 46.8 °F | 6.77 in. |
| February | 34.5 °F | 50.4 °F | 4.71 in. |
| March | 36.4 °F | 54.9 °F | 5.22 in. |
| April | 39.1 °F | 60.4 °F | 3.58 in. |
| May | 44.6 °F | 67.4 °F | 2.29 in. |
| June | 48.7 °F | 72.0 °F | 1.72 in. |
| July | 52.3 °F | 78.7 °F | 0.55 in. |
| August | 52.3 °F | 79.9 °F | 0.81 in. |
| September | 48.1 °F | 74.2 °F | 1.68 in. |
| October | 42.6 °F | 62.3 °F | 4.45 in. |
| November | 37.7 °F | 51.8 °F | 7.81 in. |
| December | 34.5 °F | 45.7 °F | 7.52 in. |
| Annual | 42.2 °F | 62 °F | 47.11 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 40-50 Days |
| Plant Hardiness Zone | Zone 8b : 15°F to 20°F |
| Plant Hardiness Zone - 2012 | Zone 8b : 15°F to 20°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |