Jamestown, Colorado has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 1.5 °C (low) to 14.9 °C (high). Annual precipitation averages 548.9 Millimeters. 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 | -6.3 °C | 4.8 °C | 19.3 mm |
| February | -6.8 °C | 5.3 °C | 28.45 mm |
| March | -3.8 °C | 9.4 °C | 50.04 mm |
| April | -1.1 °C | 12.6 °C | 80.01 mm |
| May | 3.8 °C | 17.4 °C | 80.52 mm |
| June | 8.6 °C | 24 °C | 49.78 mm |
| July | 12.3 °C | 27.5 °C | 60.96 mm |
| August | 11.4 °C | 26.3 °C | 49.53 mm |
| September | 7.3 °C | 22.3 °C | 47.75 mm |
| October | 1.7 °C | 15.2 °C | 36.58 mm |
| November | -3.1 °C | 9.2 °C | 23.88 mm |
| December | -6.5 °C | 4.7 °C | 22.1 mm |
| Annual | 1.5 °C | 14.9 °C | 548.9 mm |
| 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 : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |