Birch Bay, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 44.3 °F (low) to 57.4 °F (high). Annual precipitation averages 43.2 Inches. Birch Bay is located in USDA Plant Hardiness Zone 8b. The growing season typically runs from the last frost around Mar. 21 - Mar. 31 through the first frost around Nov. 1 - Nov. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 35.7 °F | 44.9 °F | 6.08 in. |
| February | 36.2 °F | 47.2 °F | 3.55 in. |
| March | 38.6 °F | 51.0 °F | 4.42 in. |
| April | 42.2 °F | 56.1 °F | 3.22 in. |
| May | 47.1 °F | 62.3 °F | 2.54 in. |
| June | 51.6 °F | 66.6 °F | 1.89 in. |
| July | 54.6 °F | 71.2 °F | 1.2 in. |
| August | 54.6 °F | 71.6 °F | 1.26 in. |
| September | 50.8 °F | 66.1 °F | 2.3 in. |
| October | 45.1 °F | 57.2 °F | 4.72 in. |
| November | 39.6 °F | 49.9 °F | 6.3 in. |
| December | 35.6 °F | 44.7 °F | 5.73 in. |
| Annual | 44.3 °F | 57.4 °F | 43.21 in. |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Mar. 21 - Mar. 31 |
| Average Days With Frost | 40-50 Days |
| Plant Hardiness Zone | Zone 8b : 15°F to 20°F |
| Plant Hardiness Zone - 2012 | Zone 8a : 10°F to 15°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |