Johnstown, Wyoming has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from -1 °C (low) to 15.2 °C (high). Annual precipitation averages 244.9 Millimeters. 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 | -13.5 °C | 0.9 °C | 7.62 mm |
| February | -11.5 °C | 3.4 °C | 9.14 mm |
| March | -5.6 °C | 9.9 °C | 16.26 mm |
| April | -1.3 °C | 14.2 °C | 35.56 mm |
| May | 3.8 °C | 19.3 °C | 56.39 mm |
| June | 8.2 °C | 25.7 °C | 27.69 mm |
| July | 12.1 °C | 31 °C | 16.76 mm |
| August | 10.8 °C | 29.9 °C | 14.48 mm |
| September | 6.1 °C | 23.9 °C | 22.86 mm |
| October | -0.3 °C | 15.7 °C | 20.07 mm |
| November | -7.4 °C | 7.2 °C | 10.41 mm |
| December | -12.8 °C | 0.9 °C | 7.62 mm |
| Annual | -1 °C | 15.2 °C | 244.86 mm |
| 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 : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |