Pompeys Pillar, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 0.9 °C (low) to 16.4 °C (high). Annual precipitation averages 371.9 Millimeters. 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 | -10.8 °C | 2.2 °C | 12.19 mm |
| February | -9.3 °C | 4.6 °C | 12.95 mm |
| March | -4.7 °C | 10.6 °C | 21.59 mm |
| April | 0.4 °C | 15.7 °C | 43.43 mm |
| May | 5.7 °C | 21 °C | 61.98 mm |
| June | 10.6 °C | 26.3 °C | 58.93 mm |
| July | 13.8 °C | 31.7 °C | 36.07 mm |
| August | 12.4 °C | 31.2 °C | 24.13 mm |
| September | 7.2 °C | 25.2 °C | 35.81 mm |
| October | 0.7 °C | 16.7 °C | 36.32 mm |
| November | -5.2 °C | 8.8 °C | 15.75 mm |
| December | -9.9 °C | 3.1 °C | 12.7 mm |
| Annual | 0.9 °C | 16.4 °C | 371.85 mm |
| 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 : -31.7°C to -28.9°C |
| Plant Hardiness Zone - 2012 | Zone 4a : -34.4°C to -31.7°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |