| 2023 Hardiness Zone: | Zone 5a: -20°F to -15°F Zone 4b: -25°F to -20°F Zone 4a: -30°F to -25°F |
| 2012 Hardiness Zone: | 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: | 43m - Judith Basin Grassland |
| Heat Zone Days: | Rare Over 86°F |
Annual Climate Data for ZIP Code 59457 - Lewistown, MT | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg Min Temp (°F) | 12 | 15 | 22 | 29 | 37 | 45 | 49 | 50 | 41 | 32 | 21 | 14 | 31 |
| Avg Max Temp (°F) | 32 | 36 | 42 | 52 | 62 | 70 | 79 | 79 | 68 | 57 | 42 | 34 | 54 |
| Avg Precip (In.) | .9 | .59 | 1.18 | 1.39 | 3.01 | 3.04 | 2.16 | 1.94 | 1.44 | 1.06 | .77 | .86 | 18.35 |