Glen Ullin, North Dakota has a Humid Continental Mild Summer With Dry Winters climate (Köppen classification: Dwb). Average annual temperatures range from 29.7 °F (low) to 54.3 °F (high). Annual precipitation averages 18 Inches. Glen Ullin 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 | 3.3 °F | 23.6 °F | 0.33 in. |
| February | 6.8 °F | 28.1 °F | 0.45 in. |
| March | 17.5 °F | 40.4 °F | 0.63 in. |
| April | 28.3 °F | 54.3 °F | 1.34 in. |
| May | 40.2 °F | 66.2 °F | 2.46 in. |
| June | 50.5 °F | 75.0 °F | 3.6 in. |
| July | 56.2 °F | 83.2 °F | 2.88 in. |
| August | 53.1 °F | 82.8 °F | 2.0 in. |
| September | 43.7 °F | 72.9 °F | 1.8 in. |
| October | 31.1 °F | 56.7 °F | 1.42 in. |
| November | 18.1 °F | 40.4 °F | 0.57 in. |
| December | 7.9 °F | 28.0 °F | 0.48 in. |
| Annual | 29.7 °F | 54.3 °F | 17.96 in. |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | Over 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 | Dwb - Humid Continental Mild Summer With Dry Winters |