Portland, Colorado has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -1.6 °C (low) to 15.3 °C (high). Annual precipitation averages 491 Millimeters. 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 | -12.1 °C | 3.3 °C | 33.53 mm |
| February | -9.8 °C | 5.2 °C | 36.07 mm |
| March | -5.8 °C | 9.9 °C | 45.47 mm |
| April | -2.2 °C | 13.7 °C | 48.26 mm |
| May | 1.8 °C | 19.3 °C | 39.88 mm |
| June | 5.7 °C | 25.8 °C | 20.57 mm |
| July | 9.5 °C | 27.8 °C | 50.04 mm |
| August | 8.8 °C | 26.3 °C | 53.85 mm |
| September | 4.6 °C | 22.9 °C | 48.51 mm |
| October | -1.3 °C | 16.4 °C | 42.93 mm |
| November | -6.7 °C | 9.3 °C | 36.83 mm |
| December | -12.1 °C | 3.2 °C | 35.05 mm |
| Annual | -1.6 °C | 15.3 °C | 490.99 mm |
| 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 : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Extreme Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |