| 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 5a: -20°F to -15°F Zone 4b: -25°F to -20°F Zone 4a: -30°F to -25°F | |
| 1990 Hardiness Zone: | Zone 4a: -30F to -25F | |
| Average First Frost Date: | Sep. 21 - Sep. 30 | |
| 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 59602 - Helena, MT | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg Min Temp (°F) | 12 | 17 | 24 | 32 | 41 | 48 | 53 | 52 | 42 | 33 | 22 | 13 | 32 |
| Avg Max Temp (°F) | 31 | 38 | 47 | 57 | 66 | 76 | 84 | 83 | 71 | 59 | 42 | 32 | 57 |
| Avg Precip (In.) | .48 | .34 | .59 | .84 | 1.78 | 1.76 | 1.25 | 1.23 | 1.03 | .63 | .43 | .45 | 10.82 |