Napavine, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 5.2 °C (low) to 16.7 °C (high). Annual precipitation averages 1375.9 Millimeters. Napavine is located in USDA Plant Hardiness Zone 8a. 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 | 1.1 °C | 7.9 °C | 198.88 mm |
| February | 1 °C | 10.1 °C | 139.45 mm |
| March | 2.2 °C | 12.7 °C | 149.1 mm |
| April | 3.7 °C | 15.8 °C | 111.76 mm |
| May | 6.7 °C | 19.8 °C | 70.61 mm |
| June | 8.9 °C | 22.4 °C | 53.85 mm |
| July | 10.8 °C | 26.3 °C | 16.26 mm |
| August | 10.7 °C | 27.1 °C | 22.86 mm |
| September | 8.3 °C | 23.7 °C | 48.77 mm |
| October | 5.3 °C | 16.8 °C | 129.79 mm |
| November | 2.6 °C | 10.7 °C | 221.49 mm |
| December | 0.8 °C | 7.3 °C | 213.11 mm |
| Annual | 5.2 °C | 16.7 °C | 1375.93 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 8a : -12.2°C to -9.4°C |
| Plant Hardiness Zone - 2012 | Zone 8a : -12.2°C to -9.4°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |