Casper, Wyoming has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 1 °C (low) to 15.9 °C (high). Annual precipitation averages 366.8 Millimeters. Casper 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 | -8.4 °C | 3.2 °C | 13.97 mm |
| February | -7.9 °C | 4.1 °C | 18.03 mm |
| March | -3.9 °C | 9.8 °C | 27.69 mm |
| April | -0.7 °C | 13.9 °C | 46.74 mm |
| May | 4.3 °C | 19.3 °C | 69.6 mm |
| June | 9.2 °C | 26.3 °C | 36.58 mm |
| July | 13.2 °C | 31.4 °C | 29.72 mm |
| August | 12 °C | 30.4 °C | 23.88 mm |
| September | 6.6 °C | 24.6 °C | 29.72 mm |
| October | 0.6 °C | 16.1 °C | 36.58 mm |
| November | -4.5 °C | 8.6 °C | 17.53 mm |
| December | -8.3 °C | 3.1 °C | 16.76 mm |
| Annual | 1 °C | 15.9 °C | 366.8 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 1 - May 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 | Extreme Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |