Eureka, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 32.5 °F (low) to 57.2 °F (high). Annual precipitation averages 15.5 Inches. Eureka is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Sep.11 - Sep. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 17.7 °F | 31.5 °F | 1.05 in. |
| February | 18.8 °F | 37.8 °F | 0.79 in. |
| March | 24.9 °F | 47.4 °F | 0.93 in. |
| April | 30.8 °F | 57.3 °F | 1.07 in. |
| May | 38.5 °F | 67.8 °F | 1.8 in. |
| June | 45.2 °F | 74.1 °F | 2.57 in. |
| July | 49.7 °F | 84.8 °F | 1.25 in. |
| August | 47.9 °F | 84.8 °F | 0.99 in. |
| September | 40.2 °F | 73.4 °F | 1.26 in. |
| October | 32.1 °F | 56.6 °F | 1.28 in. |
| November | 25.8 °F | 40.2 °F | 1.33 in. |
| December | 18.8 °F | 30.8 °F | 1.19 in. |
| Annual | 32.5 °F | 57.2 °F | 15.51 in. |
| Average First Frost Date | Sep.11 - Sep. 20 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5b : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |