Pompeys Pillar, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 33.6 °F (low) to 61.6 °F (high). Annual precipitation averages 14.6 Inches. Pompeys Pillar is located in USDA Plant Hardiness Zone 4b. 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 | 12.5 °F | 36.0 °F | 0.48 in. |
| February | 15.3 °F | 40.3 °F | 0.51 in. |
| March | 23.6 °F | 51.0 °F | 0.85 in. |
| April | 32.7 °F | 60.3 °F | 1.71 in. |
| May | 42.3 °F | 69.8 °F | 2.44 in. |
| June | 51.1 °F | 79.4 °F | 2.32 in. |
| July | 56.8 °F | 89.0 °F | 1.42 in. |
| August | 54.4 °F | 88.1 °F | 0.95 in. |
| September | 45.0 °F | 77.3 °F | 1.41 in. |
| October | 33.2 °F | 62.1 °F | 1.43 in. |
| November | 22.6 °F | 47.9 °F | 0.62 in. |
| December | 14.1 °F | 37.5 °F | 0.5 in. |
| Annual | 33.6 °F | 61.6 °F | 14.64 in. |
| 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 4b : -25°F to -20°F |
| Plant Hardiness Zone - 2012 | Zone 4a : -30°F to -25°F |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |