Portal, North Dakota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 27.5 °F (low) to 49.6 °F (high). Annual precipitation averages 17.5 Inches. Portal is located in USDA Plant Hardiness Zone 3b. 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 | 16.7 °F | 0.7 in. |
| February | 1.5 °F | 21.4 °F | 0.56 in. |
| March | 13.7 °F | 33.2 °F | 0.75 in. |
| April | 27.4 °F | 51.3 °F | 0.98 in. |
| May | 39.6 °F | 64.3 °F | 2.28 in. |
| June | 50.5 °F | 72.9 °F | 3.64 in. |
| July | 54.5 °F | 78.7 °F | 2.64 in. |
| August | 52.0 °F | 79.1 °F | 1.66 in. |
| September | 42.7 °F | 69.0 °F | 1.44 in. |
| October | 30.0 °F | 52.8 °F | 1.39 in. |
| November | 16.3 °F | 34.6 °F | 0.77 in. |
| December | 4.0 °F | 21.5 °F | 0.72 in. |
| Annual | 27.5 °F | 49.6 °F | 17.53 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 3b : -35°F to -30°F |
| Plant Hardiness Zone - 2012 | Zone 3b : -35°F to -30°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |