Hays, Montana has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 0.1 °C (low) to 13.2 °C (high). Annual precipitation averages 438.2 Millimeters. Hays is located in USDA Plant Hardiness Zone 4b. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.2 °C | 0.6 °C | 16.26 mm |
| February | -9.9 °C | 1.7 °C | 13.97 mm |
| March | -5.8 °C | 6.7 °C | 20.57 mm |
| April | -0.8 °C | 11.9 °C | 35.31 mm |
| May | 4.3 °C | 17 °C | 75.95 mm |
| June | 8.8 °C | 21.8 °C | 91.69 mm |
| July | 11.9 °C | 27.7 °C | 51.82 mm |
| August | 11.4 °C | 27.4 °C | 32.77 mm |
| September | 6.3 °C | 21.2 °C | 32 mm |
| October | 0.6 °C | 13.6 °C | 36.07 mm |
| November | -5.2 °C | 6.3 °C | 16.51 mm |
| December | -9.6 °C | 2.1 °C | 15.24 mm |
| Annual | 0.1 °C | 13.2 °C | 438.16 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 4b : -31.7°C to -28.9°C |
| Plant Hardiness Zone - 2012 | Zone 4a : -34.4°C to -31.7°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |