Portland, North Dakota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 30 °F (low) to 50.6 °F (high). Annual precipitation averages 23.1 Inches. Portland is located in USDA Plant Hardiness Zone 4a. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -2.0 °F | 15.6 °F | 0.58 in. |
| February | 1.7 °F | 20.8 °F | 0.52 in. |
| March | 15.2 °F | 33.4 °F | 0.95 in. |
| April | 30.0 °F | 51.7 °F | 1.2 in. |
| May | 42.9 °F | 66.1 °F | 2.86 in. |
| June | 54.6 °F | 75.8 °F | 4.22 in. |
| July | 58.1 °F | 80.3 °F | 3.93 in. |
| August | 55.1 °F | 79.2 °F | 2.86 in. |
| September | 46.1 °F | 70.8 °F | 2.44 in. |
| October | 33.7 °F | 54.9 °F | 1.96 in. |
| November | 19.2 °F | 36.7 °F | 0.83 in. |
| December | 5.8 °F | 21.7 °F | 0.79 in. |
| Annual | 30 °F | 50.6 °F | 23.14 in. |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 4a : -30°F to -25°F |
| Plant Hardiness Zone - 2012 | Zone 4a : -30°F to -25°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |