Johnstown, Wyoming has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 30.3 °F (low) to 59.3 °F (high). Annual precipitation averages 9.6 Inches. Johnstown is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 7.7 °F | 33.7 °F | 0.3 in. |
| February | 11.3 °F | 38.1 °F | 0.36 in. |
| March | 22.0 °F | 49.8 °F | 0.64 in. |
| April | 29.7 °F | 57.5 °F | 1.4 in. |
| May | 38.9 °F | 66.8 °F | 2.22 in. |
| June | 46.8 °F | 78.2 °F | 1.09 in. |
| July | 53.7 °F | 87.8 °F | 0.66 in. |
| August | 51.5 °F | 85.8 °F | 0.57 in. |
| September | 42.9 °F | 75.0 °F | 0.9 in. |
| October | 31.4 °F | 60.3 °F | 0.79 in. |
| November | 18.7 °F | 45.0 °F | 0.41 in. |
| December | 9.0 °F | 33.7 °F | 0.3 in. |
| Annual | 30.3 °F | 59.3 °F | 9.64 in. |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5a : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 4b : -25°F to -20°F |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |