Jamestown, Colorado has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 34.7 °F (low) to 58.8 °F (high). Annual precipitation averages 21.6 Inches. Jamestown is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Sep.1 - Sep. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 20.7 °F | 40.7 °F | 0.76 in. |
| February | 19.7 °F | 41.6 °F | 1.12 in. |
| March | 25.2 °F | 49.0 °F | 1.97 in. |
| April | 30.1 °F | 54.6 °F | 3.15 in. |
| May | 38.9 °F | 63.3 °F | 3.17 in. |
| June | 47.4 °F | 75.2 °F | 1.96 in. |
| July | 54.2 °F | 81.5 °F | 2.4 in. |
| August | 52.6 °F | 79.4 °F | 1.95 in. |
| September | 45.2 °F | 72.1 °F | 1.88 in. |
| October | 35.0 °F | 59.4 °F | 1.44 in. |
| November | 26.5 °F | 48.5 °F | 0.94 in. |
| December | 20.3 °F | 40.5 °F | 0.87 in. |
| Annual | 34.7 °F | 58.8 °F | 21.61 in. |
| Average First Frost Date | Sep.1 - Sep. 10 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 6a : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |