Johnstown, Colorado has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 34.4 °F (low) to 64 °F (high). Annual precipitation averages 13.6 Inches. Johnstown is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 14.0 °F | 41.7 °F | 0.28 in. |
| February | 16.6 °F | 44.2 °F | 0.43 in. |
| March | 25.2 °F | 55.1 °F | 0.98 in. |
| April | 32.5 °F | 61.7 °F | 1.48 in. |
| May | 42.7 °F | 70.5 °F | 2.51 in. |
| June | 52.1 °F | 82.6 °F | 1.63 in. |
| July | 57.3 °F | 88.6 °F | 1.66 in. |
| August | 54.9 °F | 86.4 °F | 1.29 in. |
| September | 46.1 °F | 78.8 °F | 1.33 in. |
| October | 33.9 °F | 64.9 °F | 0.9 in. |
| November | 22.9 °F | 51.7 °F | 0.56 in. |
| December | 14.1 °F | 41.5 °F | 0.53 in. |
| Annual | 34.4 °F | 64 °F | 13.58 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5b : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |