Jamestown, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 6.5 °C (low) to 13.8 °C (high). Annual precipitation averages 447 Millimeters. Jamestown 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. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 2.8 °C | 8 °C | 57.4 mm |
| February | 2.7 °C | 8.9 °C | 41.91 mm |
| March | 3.7 °C | 10.7 °C | 42.16 mm |
| April | 5.3 °C | 13.2 °C | 33.02 mm |
| May | 7.8 °C | 16 °C | 29.72 mm |
| June | 9.8 °C | 17.7 °C | 22.86 mm |
| July | 10.9 °C | 19.4 °C | 13.97 mm |
| August | 10.9 °C | 19.8 °C | 13.46 mm |
| September | 9.6 °C | 18.7 °C | 21.59 mm |
| October | 6.9 °C | 14.4 °C | 42.42 mm |
| November | 4.4 °C | 10.3 °C | 68.07 mm |
| December | 2.7 °C | 7.9 °C | 60.45 mm |
| Annual | 6.5 °C | 13.8 °C | 447.03 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 75-100 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 | Moderate Drought |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |