Spearfish, South Dakota has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 1.4 °C (low) to 14.9 °C (high). Annual precipitation averages 612.9 Millimeters. Spearfish is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -9.6 °C | 2.6 °C | 18.54 mm |
| February | -9 °C | 3.2 °C | 26.16 mm |
| March | -4.7 °C | 8.4 °C | 32.51 mm |
| April | -0.2 °C | 13.2 °C | 66.8 mm |
| May | 5.4 °C | 18.6 °C | 105.41 mm |
| June | 10.7 °C | 24.6 °C | 99.31 mm |
| July | 14.3 °C | 29.4 °C | 62.23 mm |
| August | 13.2 °C | 28.9 °C | 49.28 mm |
| September | 8.2 °C | 23.6 °C | 41.91 mm |
| October | 1.6 °C | 15.3 °C | 56.39 mm |
| November | -4.3 °C | 8.3 °C | 25.15 mm |
| December | -8.7 °C | 3.1 °C | 29.21 mm |
| Annual | 1.4 °C | 14.9 °C | 612.9 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°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 |