Marion, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 25.7 °F (low) to 53.9 °F (high). Annual precipitation averages 18.1 Inches. 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 | 11.7 °F | 32.6 °F | 1.73 in. |
| February | 11.5 °F | 36.1 °F | 1.11 in. |
| March | 17.9 °F | 44.5 °F | 1.48 in. |
| April | 24.4 °F | 51.6 °F | 1.43 in. |
| May | 31.7 °F | 61.6 °F | 1.81 in. |
| June | 37.8 °F | 68.7 °F | 2.47 in. |
| July | 41.5 °F | 79.9 °F | 1.01 in. |
| August | 39.8 °F | 79.6 °F | 0.88 in. |
| September | 33.3 °F | 68.5 °F | 1.49 in. |
| October | 25.6 °F | 52.9 °F | 1.42 in. |
| November | 19.4 °F | 39.4 °F | 1.41 in. |
| December | 14.1 °F | 31.4 °F | 1.86 in. |
| Annual | 25.7 °F | 53.9 °F | 18.1 in. |
| 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 : -25°F to -20°F |
| Plant Hardiness Zone - 2012 | Zone 4b : -25°F to -20°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |