Montesano, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 42.6 °F (low) to 59.8 °F (high). Annual precipitation averages 78.4 Inches. Montesano 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 | 36.3 °F | 47.4 °F | 12.72 in. |
| February | 35.3 °F | 50.0 °F | 6.44 in. |
| March | 37.0 °F | 53.7 °F | 9.46 in. |
| April | 39.5 °F | 57.6 °F | 6.37 in. |
| May | 44.6 °F | 63.5 °F | 3.32 in. |
| June | 48.7 °F | 67.2 °F | 2.57 in. |
| July | 52.1 °F | 72.6 °F | 0.98 in. |
| August | 51.9 °F | 76.8 °F | 1.51 in. |
| September | 48.7 °F | 70.5 °F | 3.01 in. |
| October | 43.1 °F | 60.5 °F | 8.03 in. |
| November | 38.1 °F | 51.8 °F | 11.36 in. |
| December | 35.3 °F | 46.4 °F | 12.61 in. |
| Annual | 42.6 °F | 59.8 °F | 78.38 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 50-75 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 |