| 2023 Hardiness Zone: | Zone 5a: -20°F to -15°F Zone 4b: -25°F to -20°F Zone 5b: -15°F to -10°F | |
| 2012 Hardiness Zone: | Zone 4b: -25°F to -20°F | |
| 1990 Hardiness Zone: | Zone 4a: -30F to -25F | |
| Average First Frost Date: | Sep.11 - Sep. 20 | |
| Average Last Frost Date: | May 21 - May 31 | |
| Koppen-Geiger Climate Zone: | Dfb - Humid Continental Mild Summer, Wet All Year | |
| Ecoregion: | 17w - Townsend Basin | |
| Current Drought Status: | Exceptional Drought | |
| Heat Zone Days: | 1 - 7 days Over 86°F |
Annual Climate Data for ZIP Code 59635 - East Helena, MT | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg Min Temp (°F) | 11 | 16 | 23 | 31 | 40 | 47 | 52 | 51 | 41 | 32 | 21 | 12 | 31 |
| Avg Max Temp (°F) | 31 | 37 | 47 | 57 | 66 | 75 | 83 | 83 | 71 | 58 | 42 | 32 | 57 |
| Avg Precip (In.) | .5 | .38 | .64 | .93 | 1.82 | 1.83 | 1.3 | 1.31 | 1.06 | .66 | .48 | .48 | 11.38 |