Marion, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -3.5 °C (low) to 12.2 °C (high). Annual precipitation averages 459.7 Millimeters. Marion 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 Sep.1 - Sep. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.3 °C | 0.3 °C | 43.94 mm |
| February | -11.4 °C | 2.3 °C | 28.19 mm |
| March | -7.8 °C | 6.9 °C | 37.59 mm |
| April | -4.2 °C | 10.9 °C | 36.32 mm |
| May | -0.2 °C | 16.4 °C | 45.97 mm |
| June | 3.2 °C | 20.4 °C | 62.74 mm |
| July | 5.3 °C | 26.6 °C | 25.65 mm |
| August | 4.3 °C | 26.4 °C | 22.35 mm |
| September | 0.7 °C | 20.3 °C | 37.85 mm |
| October | -3.6 °C | 11.6 °C | 36.07 mm |
| November | -7 °C | 4.1 °C | 35.81 mm |
| December | -9.9 °C | -0.3 °C | 47.24 mm |
| Annual | -3.5 °C | 12.2 °C | 459.72 mm |
| Average First Frost Date | Sep.1 - Sep. 10 |
| 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 | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |