Mullan, Idaho has a Humid Continental Climate - Dry Cool Summer climate (Köppen classification: Dsb). Average annual temperatures range from 33.1 °F (low) to 54.9 °F (high). Annual precipitation averages 37 Inches. Mullan is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around May 21 - May 31 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 22.2 °F | 33.9 °F | 3.92 in. |
| February | 22.1 °F | 37.4 °F | 3.86 in. |
| March | 25.5 °F | 45.4 °F | 4.03 in. |
| April | 30.9 °F | 52.6 °F | 2.91 in. |
| May | 37.2 °F | 63.0 °F | 2.87 in. |
| June | 43.3 °F | 69.7 °F | 3.12 in. |
| July | 47.5 °F | 80.2 °F | 1.06 in. |
| August | 46.8 °F | 80.2 °F | 1.04 in. |
| September | 40.4 °F | 69.9 °F | 1.54 in. |
| October | 33.0 °F | 54.1 °F | 3.48 in. |
| November | 26.8 °F | 40.0 °F | 4.53 in. |
| December | 21.5 °F | 32.4 °F | 4.68 in. |
| Annual | 33.1 °F | 54.9 °F | 37.04 in. |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 21 - May 31 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 6b : -5°F to 0°F |
| Plant Hardiness Zone - 2012 | Zone 6a : -10°F to -5°F |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dsb - Humid Continental Climate - Dry Cool Summer |