Portland, Colorado has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 29.1 °F (low) to 59.5 °F (high). Annual precipitation averages 19.3 Inches. Portland is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Jun. 1 - Jun. 10 through the first frost around Sep.1 - Sep. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 10.2 °F | 37.9 °F | 1.32 in. |
| February | 14.4 °F | 41.4 °F | 1.42 in. |
| March | 21.6 °F | 49.8 °F | 1.79 in. |
| April | 28.0 °F | 56.6 °F | 1.9 in. |
| May | 35.2 °F | 66.8 °F | 1.57 in. |
| June | 42.3 °F | 78.4 °F | 0.81 in. |
| July | 49.1 °F | 82.1 °F | 1.97 in. |
| August | 47.9 °F | 79.4 °F | 2.12 in. |
| September | 40.3 °F | 73.2 °F | 1.91 in. |
| October | 29.7 °F | 61.5 °F | 1.69 in. |
| November | 20.0 °F | 48.7 °F | 1.45 in. |
| December | 10.3 °F | 37.8 °F | 1.38 in. |
| Annual | 29.1 °F | 59.5 °F | 19.33 in. |
| Average First Frost Date | Sep.1 - Sep. 10 |
| Average Last Frost Date | Jun. 1 - Jun. 10 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 5b : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |