Hanna, Wyoming has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -1.6 °C (low) to 13.4 °C (high). Annual precipitation averages 321.1 Millimeters. Hanna is located in USDA Plant Hardiness Zone 4b. The growing season typically runs from the last frost around May 21 - May 31 through the first frost around Aug. 21 - Aug. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -10.8 °C | 0.6 °C | 17.02 mm |
| February | -10.2 °C | 1.7 °C | 17.02 mm |
| March | -6.1 °C | 6.8 °C | 22.61 mm |
| April | -2.9 °C | 11.4 °C | 36.58 mm |
| May | 1.6 °C | 17.3 °C | 48.26 mm |
| June | 6.1 °C | 24 °C | 27.94 mm |
| July | 9.7 °C | 28.5 °C | 24.13 mm |
| August | 8.6 °C | 27.3 °C | 23.88 mm |
| September | 3.9 °C | 22.2 °C | 25.4 mm |
| October | -1.7 °C | 14.1 °C | 34.04 mm |
| November | -6.5 °C | 6.2 °C | 23.62 mm |
| December | -10.9 °C | 0.6 °C | 20.57 mm |
| Annual | -1.6 °C | 13.4 °C | 321.07 mm |
| Average First Frost Date | Aug. 21 - Aug. 31 |
| Average Last Frost Date | May 21 - May 31 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 4b : -31.7°C to -28.9°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |