| 2023 Hardiness Zone: | Zone 5a: -20°F to -15°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 5b: -15°F to -10°F |
| 1990 Hardiness Zone: | Zone 4b: -25F to -20F |
| Average First Frost Date: | Oct. 1 - Oct. 10 |
| Average Last Frost Date: | May 21 - May 31 |
| Koppen-Geiger Climate Zone: | Dfb - Humid Continental Mild Summer, Wet All Year |
| Ecoregion: | 53c - Southeastern Wisconsin Savannah and Till Plain |
| Heat Zone Days: | Rare Over 86°F |
Annual Climate Data for ZIP Code 53561 - Merrimac, WI | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg Min Temp (°F) | 5 | 10 | 22 | 34 | 45 | 55 | 59 | 57 | 48 | 37 | 25 | 12 | 34 |
| Avg Max Temp (°F) | 25 | 31 | 42 | 56 | 69 | 78 | 82 | 80 | 71 | 60 | 43 | 30 | 56 |
| Avg Precip (In.) | 1.11 | 1.09 | 2.06 | 3.29 | 3.32 | 4.07 | 4.09 | 4.33 | 3.42 | 2.31 | 2.22 | 1.27 | 32.59 |