Montesano, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 5.9 °C (low) to 15.5 °C (high). Annual precipitation averages 1990.8 Millimeters. 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 | 2.4 °C | 8.6 °C | 323.09 mm |
| February | 1.8 °C | 10 °C | 163.58 mm |
| March | 2.8 °C | 12.1 °C | 240.28 mm |
| April | 4.2 °C | 14.2 °C | 161.8 mm |
| May | 7 °C | 17.5 °C | 84.33 mm |
| June | 9.3 °C | 19.6 °C | 65.28 mm |
| July | 11.2 °C | 22.6 °C | 24.89 mm |
| August | 11.1 °C | 24.9 °C | 38.35 mm |
| September | 9.3 °C | 21.4 °C | 76.45 mm |
| October | 6.2 °C | 15.8 °C | 203.96 mm |
| November | 3.4 °C | 11 °C | 288.54 mm |
| December | 1.8 °C | 8 °C | 320.29 mm |
| Annual | 5.9 °C | 15.5 °C | 1990.84 mm |
| 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 : -9.4°C to -6.7°C |
| Plant Hardiness Zone - 2012 | Zone 8b : -9.4°C to -6.7°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |