Castle Rock, Colorado has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 1.5 °C (low) to 17.6 °C (high). Annual precipitation averages 458.5 Millimeters. Castle Rock is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -8.3 °C | 7.2 °C | 15.75 mm |
| February | -7.6 °C | 7.5 °C | 17.02 mm |
| March | -3.7 °C | 12 °C | 38.1 mm |
| April | -0.3 °C | 15.4 °C | 58.42 mm |
| May | 4.8 °C | 20.4 °C | 55.63 mm |
| June | 10 °C | 26.9 °C | 54.61 mm |
| July | 13.4 °C | 30.3 °C | 59.69 mm |
| August | 12.5 °C | 29 °C | 62.23 mm |
| September | 8 °C | 25.2 °C | 36.58 mm |
| October | 1.3 °C | 18.3 °C | 24.89 mm |
| November | -3.9 °C | 11.7 °C | 19.3 mm |
| December | -8.3 °C | 6.8 °C | 16.26 mm |
| Annual | 1.5 °C | 17.6 °C | 458.48 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |