Hamilton, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 32.4 °F (low) to 58.9 °F (high). Annual precipitation averages 13.8 Inches. Hamilton 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 | 18.6 °F | 35.9 °F | 1.0 in. |
| February | 20.5 °F | 40.6 °F | 1.07 in. |
| March | 25.6 °F | 49.8 °F | 0.97 in. |
| April | 31.2 °F | 57.9 °F | 1.01 in. |
| May | 38.0 °F | 67.2 °F | 1.56 in. |
| June | 44.4 °F | 74.4 °F | 1.73 in. |
| July | 49.2 °F | 85.6 °F | 1.0 in. |
| August | 47.5 °F | 84.4 °F | 0.86 in. |
| September | 40.2 °F | 74.0 °F | 0.83 in. |
| October | 31.7 °F | 58.9 °F | 0.99 in. |
| November | 23.9 °F | 43.4 °F | 1.45 in. |
| December | 18.3 °F | 34.4 °F | 1.32 in. |
| Annual | 32.4 °F | 58.9 °F | 13.79 in. |
| Average First Frost Date | Sep.11 - Sep. 20 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 5b : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |