Fort Smith, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2.3 °C (low) to 16.8 °C (high). Annual precipitation averages 425.7 Millimeters. Fort Smith 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 | -8.3 °C | 3.8 °C | 19.05 mm |
| February | -7.3 °C | 5.4 °C | 19.3 mm |
| March | -3.1 °C | 10.7 °C | 30.48 mm |
| April | 1.5 °C | 15.4 °C | 56.39 mm |
| May | 6.3 °C | 20.8 °C | 67.06 mm |
| June | 10.9 °C | 26.5 °C | 53.09 mm |
| July | 14.4 °C | 32.2 °C | 28.7 mm |
| August | 13.2 °C | 31.4 °C | 20.07 mm |
| September | 8.4 °C | 25.3 °C | 42.16 mm |
| October | 2.3 °C | 16.9 °C | 48.51 mm |
| November | -3.3 °C | 9.2 °C | 23.37 mm |
| December | -7.4 °C | 4.2 °C | 17.53 mm |
| Annual | 2.3 °C | 16.8 °C | 425.71 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 100-125 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 | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |