Friday Harbor, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 6.6 °C (low) to 13.9 °C (high). Annual precipitation averages 627.9 Millimeters. Friday Harbor is located in USDA Plant Hardiness Zone 9a. The growing season typically runs from the last frost around Mar. 21 - Mar. 31 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 3.1 °C | 7.6 °C | 90.93 mm |
| February | 2.9 °C | 8.4 °C | 56.39 mm |
| March | 3.9 °C | 10.3 °C | 56.39 mm |
| April | 5.3 °C | 12.9 °C | 43.43 mm |
| May | 7.6 °C | 16.2 °C | 32 mm |
| June | 9.8 °C | 18.7 °C | 23.11 mm |
| July | 11.1 °C | 21.2 °C | 16.26 mm |
| August | 11.2 °C | 21.5 °C | 18.03 mm |
| September | 9.7 °C | 18.9 °C | 30.99 mm |
| October | 7.2 °C | 13.9 °C | 75.69 mm |
| November | 4.7 °C | 9.9 °C | 93.73 mm |
| December | 3.1 °C | 7.4 °C | 90.93 mm |
| Annual | 6.6 °C | 13.9 °C | 627.88 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Mar. 21 - Mar. 31 |
| Average Days With Frost | 40-50 Days |
| Plant Hardiness Zone | Zone 9a : -6.7°C to -3.9°C |
| Plant Hardiness Zone - 2012 | Zone 9a : -6.7°C to -3.9°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |