Lyman, Wyoming has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from -2 °C (low) to 13.5 °C (high). Annual precipitation averages 263.7 Millimeters. Lyman is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around Jun. 1 - Jun. 10 through the first frost around Sep.1 - Sep. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -12.1 °C | 0.1 °C | 13.21 mm |
| February | -11.3 °C | 1.2 °C | 13.72 mm |
| March | -6.4 °C | 6.8 °C | 17.27 mm |
| April | -2.9 °C | 12.2 °C | 26.92 mm |
| May | 1.6 °C | 17.7 °C | 35.56 mm |
| June | 5.7 °C | 23.8 °C | 23.88 mm |
| July | 9.6 °C | 28.5 °C | 22.35 mm |
| August | 8.7 °C | 27.6 °C | 20.32 mm |
| September | 4 °C | 22.4 °C | 29.97 mm |
| October | -1.4 °C | 14.8 °C | 25.91 mm |
| November | -7.2 °C | 6.1 °C | 19.56 mm |
| December | -11.8 °C | 0.2 °C | 14.99 mm |
| Annual | -2 °C | 13.5 °C | 263.66 mm |
| Average First Frost Date | Sep.1 - Sep. 10 |
| Average Last Frost Date | Jun. 1 - Jun. 10 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 5a : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |