Castle Rock, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 43.3 °F (low) to 61.6 °F (high). Annual precipitation averages 47.3 Inches. Castle Rock 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 | 35.6 °F | 46.8 °F | 6.57 in. |
| February | 34.8 °F | 50.5 °F | 4.7 in. |
| March | 37.5 °F | 54.9 °F | 4.96 in. |
| April | 40.7 °F | 59.8 °F | 4.11 in. |
| May | 46.0 °F | 66.5 °F | 2.81 in. |
| June | 50.1 °F | 70.6 °F | 1.96 in. |
| July | 53.8 °F | 77.0 °F | 0.57 in. |
| August | 53.7 °F | 78.4 °F | 0.85 in. |
| September | 49.8 °F | 73.8 °F | 1.85 in. |
| October | 43.9 °F | 62.6 °F | 4.43 in. |
| November | 38.8 °F | 52.0 °F | 7.2 in. |
| December | 35.1 °F | 45.7 °F | 7.32 in. |
| Annual | 43.3 °F | 61.6 °F | 47.33 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 |