Glen Ullin, North Dakota has a Humid Continental Mild Summer With Dry Winters climate (Köppen classification: Dwb). Average annual temperatures range from -1.3 °C (low) to 12.4 °C (high). Annual precipitation averages 456.2 Millimeters. 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 | -15.9 °C | -4.7 °C | 8.38 mm |
| February | -14 °C | -2.2 °C | 11.43 mm |
| March | -8.1 °C | 4.7 °C | 16 mm |
| April | -2.1 °C | 12.4 °C | 34.04 mm |
| May | 4.6 °C | 19 °C | 62.48 mm |
| June | 10.3 °C | 23.9 °C | 91.44 mm |
| July | 13.4 °C | 28.4 °C | 73.15 mm |
| August | 11.7 °C | 28.2 °C | 50.8 mm |
| September | 6.5 °C | 22.7 °C | 45.72 mm |
| October | -0.5 °C | 13.7 °C | 36.07 mm |
| November | -7.7 °C | 4.7 °C | 14.48 mm |
| December | -13.4 °C | -2.2 °C | 12.19 mm |
| Annual | -1.3 °C | 12.4 °C | 456.18 mm |
| 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 : -34.4°C to -31.7°C |
| Plant Hardiness Zone - 2012 | Zone 4a : -34.4°C to -31.7°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dwb - Humid Continental Mild Summer With Dry Winters |