South Glastonbury, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 30.8 °F (low) to 56.6 °F (high). Annual precipitation averages 15.4 Inches. South Glastonbury 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.1 - Sep. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 15.2 °F | 34.3 °F | 0.54 in. |
| February | 15.4 °F | 36.9 °F | 0.6 in. |
| March | 22.3 °F | 45.9 °F | 0.92 in. |
| April | 28.9 °F | 54.4 °F | 1.68 in. |
| May | 36.6 °F | 63.3 °F | 2.25 in. |
| June | 43.4 °F | 72.6 °F | 2.42 in. |
| July | 49.4 °F | 83.2 °F | 1.53 in. |
| August | 47.7 °F | 82.7 °F | 1.27 in. |
| September | 41.2 °F | 72.6 °F | 1.26 in. |
| October | 31.9 °F | 57.5 °F | 1.3 in. |
| November | 22.4 °F | 42.7 °F | 0.85 in. |
| December | 15.0 °F | 33.4 °F | 0.73 in. |
| Annual | 30.8 °F | 56.6 °F | 15.35 in. |
| Average First Frost Date | Sep.1 - Sep. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 5a : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 4b : -25°F to -20°F |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |