Fern Prairie, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 42.9 °F (low) to 62.5 °F (high). Annual precipitation averages 58.9 Inches. Fern Prairie 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 | 34.4 °F | 45.8 °F | 7.77 in. |
| February | 34.7 °F | 49.8 °F | 5.56 in. |
| March | 37.0 °F | 54.7 °F | 6.69 in. |
| April | 40.4 °F | 60.8 °F | 5.14 in. |
| May | 45.6 °F | 68.2 °F | 4.04 in. |
| June | 49.7 °F | 72.8 °F | 2.95 in. |
| July | 53.7 °F | 80.7 °F | 0.76 in. |
| August | 53.7 °F | 81.5 °F | 0.76 in. |
| September | 49.6 °F | 75.3 °F | 2.42 in. |
| October | 43.5 °F | 63.1 °F | 5.72 in. |
| November | 38.2 °F | 51.9 °F | 8.37 in. |
| December | 34.2 °F | 45.1 °F | 8.67 in. |
| Annual | 42.9 °F | 62.5 °F | 58.85 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 | Abnormally Dry |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |