Portal, North Dakota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -2.5 °C (low) to 9.8 °C (high). Annual precipitation averages 445.3 Millimeters. 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 | -18.9 °C | -8.5 °C | 17.78 mm |
| February | -16.9 °C | -5.9 °C | 14.22 mm |
| March | -10.2 °C | 0.7 °C | 19.05 mm |
| April | -2.6 °C | 10.7 °C | 24.89 mm |
| May | 4.2 °C | 17.9 °C | 57.91 mm |
| June | 10.3 °C | 22.7 °C | 92.46 mm |
| July | 12.5 °C | 25.9 °C | 67.06 mm |
| August | 11.1 °C | 26.2 °C | 42.16 mm |
| September | 5.9 °C | 20.6 °C | 36.58 mm |
| October | -1.1 °C | 11.6 °C | 35.31 mm |
| November | -8.7 °C | 1.4 °C | 19.56 mm |
| December | -15.6 °C | -5.8 °C | 18.29 mm |
| Annual | -2.5 °C | 9.8 °C | 445.27 mm |
| 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 : -37.2°C to -34.4°C |
| Plant Hardiness Zone - 2012 | Zone 3b : -37.2°C to -34.4°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |