Eureka, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 0.3 °C (low) to 14 °C (high). Annual precipitation averages 394 Millimeters. 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 | -7.9 °C | -0.3 °C | 26.67 mm |
| February | -7.3 °C | 3.2 °C | 20.07 mm |
| March | -3.9 °C | 8.6 °C | 23.62 mm |
| April | -0.7 °C | 14.1 °C | 27.18 mm |
| May | 3.6 °C | 19.9 °C | 45.72 mm |
| June | 7.3 °C | 23.4 °C | 65.28 mm |
| July | 9.8 °C | 29.3 °C | 31.75 mm |
| August | 8.8 °C | 29.3 °C | 25.15 mm |
| September | 4.6 °C | 23 °C | 32 mm |
| October | 0.1 °C | 13.7 °C | 32.51 mm |
| November | -3.4 °C | 4.6 °C | 33.78 mm |
| December | -7.3 °C | -0.7 °C | 30.23 mm |
| Annual | 0.3 °C | 14 °C | 393.96 mm |
| 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 : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |