| 2023 Hardiness Zone: | Zone 6b: -5°F to 0°F Zone 7a: 0°F to 5°F | |
| 2012 Hardiness Zone: | Zone 6a: -10°F to -5°F Zone 6b: -5°F to 0°F | |
| 1990 Hardiness Zone: | Zone 6b: -5F to 0F | |
| Average First Frost Date: | Oct. 11 - Oct. 20 | |
| Average Last Frost Date: | May 1 - May 10 | |
| Koppen-Geiger Climate Zone: | Dfa - Humid Continental Hot Summers | |
| Ecoregion: | 67a - Northern Limestone/Dolomite Valleys | |
| Current Drought Status: | Exceptional Drought | |
| Heat Zone Days: | Rare Over 86°F |
Annual Climate Data for ZIP Code 19539 - Mertztown, PA | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg Min Temp (°F) | 18 | 20 | 29 | 37 | 47 | 57 | 61 | 60 | 52 | 40 | 32 | 24 | 40 |
| Avg Max Temp (°F) | 37 | 40 | 49 | 61 | 71 | 80 | 84 | 83 | 75 | 64 | 52 | 41 | 61 |
| Avg Precip (In.) | 3.89 | 2.86 | 3.77 | 3.79 | 4.74 | 4.42 | 4.26 | 4.32 | 4.57 | 3.68 | 3.92 | 3.64 | 47.86 |