Jefferson City, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 28.9 °F (low) to 55.8 °F (high). Annual precipitation averages 17 Inches. Jefferson City 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 Aug. 21 - Aug. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 12.5 °F | 34.2 °F | 0.73 in. |
| February | 14.1 °F | 37.0 °F | 0.85 in. |
| March | 20.8 °F | 45.5 °F | 0.8 in. |
| April | 27.5 °F | 53.4 °F | 1.7 in. |
| May | 35.8 °F | 62.4 °F | 2.66 in. |
| June | 42.5 °F | 71.4 °F | 3.01 in. |
| July | 47.8 °F | 82.4 °F | 1.31 in. |
| August | 45.5 °F | 81.6 °F | 1.38 in. |
| September | 38.5 °F | 70.7 °F | 1.41 in. |
| October | 29.0 °F | 56.2 °F | 1.43 in. |
| November | 20.1 °F | 42.1 °F | 0.77 in. |
| December | 12.5 °F | 33.2 °F | 0.91 in. |
| Annual | 28.9 °F | 55.8 °F | 16.96 in. |
| Average First Frost Date | Aug. 21 - Aug. 31 |
| 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 | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |