Sedan, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -2.2 °C (low) to 12.4 °C (high). Annual precipitation averages 596.9 Millimeters. Sedan is located in USDA Plant Hardiness Zone 4b. The growing season typically runs from the last frost around Jun. 11 - Jun. 20 through the first frost around Sep.11 - Sep. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -10.2 °C | 1.4 °C | 33.78 mm |
| February | -9.9 °C | 2.1 °C | 32.51 mm |
| March | -6.4 °C | 6.3 °C | 38.61 mm |
| April | -3.3 °C | 10.8 °C | 69.6 mm |
| May | 0.8 °C | 15.6 °C | 80.52 mm |
| June | 4.6 °C | 20.6 °C | 89.92 mm |
| July | 7.2 °C | 26.7 °C | 42.16 mm |
| August | 6.4 °C | 26.4 °C | 37.85 mm |
| September | 3.1 °C | 20.6 °C | 44.7 mm |
| October | -1.6 °C | 12.4 °C | 48.01 mm |
| November | -6.5 °C | 5.4 °C | 40.64 mm |
| December | -10.2 °C | 0.5 °C | 38.61 mm |
| Annual | -2.2 °C | 12.4 °C | 596.91 mm |
| Average First Frost Date | Sep.11 - Sep. 20 |
| Average Last Frost Date | Jun. 11 - Jun. 20 |
| Average Days With Frost | Over 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 | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |