Trego, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -1.1 °C (low) to 12.8 °C (high). Annual precipitation averages 438.4 Millimeters. Trego is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Sep.11 - Sep. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -9.2 °C | -1.1 °C | 30.48 mm |
| February | -8.7 °C | 2.2 °C | 22.35 mm |
| March | -5.3 °C | 7.2 °C | 25.91 mm |
| April | -1.9 °C | 12.6 °C | 33.53 mm |
| May | 2.3 °C | 18.6 °C | 51.82 mm |
| June | 6.1 °C | 22.2 °C | 81.53 mm |
| July | 8.2 °C | 27.9 °C | 36.83 mm |
| August | 7.3 °C | 27.9 °C | 21.08 mm |
| September | 2.9 °C | 21.5 °C | 34.54 mm |
| October | -1.4 °C | 12.3 °C | 29.46 mm |
| November | -4.7 °C | 3.8 °C | 35.31 mm |
| December | -8.6 °C | -1.4 °C | 35.56 mm |
| Annual | -1.1 °C | 12.8 °C | 438.4 mm |
| Average First Frost Date | Sep.11 - Sep. 20 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 5a : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |