New Castle, Colorado has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -0.1 °C (low) to 16.8 °C (high). Annual precipitation averages 377.7 Millimeters. New Castle is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.1 °C | 2.7 °C | 28.19 mm |
| February | -8.1 °C | 5.8 °C | 28.7 mm |
| March | -4 °C | 11.8 °C | 28.96 mm |
| April | -0.7 °C | 15.9 °C | 39.12 mm |
| May | 3.3 °C | 21.3 °C | 40.64 mm |
| June | 7.6 °C | 27.9 °C | 20.57 mm |
| July | 11.6 °C | 31.2 °C | 26.67 mm |
| August | 10.6 °C | 29.7 °C | 28.96 mm |
| September | 5.8 °C | 25.2 °C | 42.16 mm |
| October | -0.3 °C | 17.9 °C | 41.66 mm |
| November | -5.7 °C | 9.9 °C | 27.69 mm |
| December | -10.7 °C | 2.8 °C | 24.38 mm |
| Annual | -0.1 °C | 16.8 °C | 377.7 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Exceptional Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |