| 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 | |
| 1990 Hardiness Zone: | Zone 4b: -25F to -20F | |
| Average First Frost Date: | Oct. 1 - Oct. 10 | |
| Average Last Frost Date: | May 11 - May 20 | |
| Koppen-Geiger Climate Zone: | Dfa - Humid Continental Hot Summers | |
| Ecoregion: | 47e - Steeply Rolling Loess Prairies | |
| Current Drought Status: | Exceptional Drought | |
| Heat Zone Days: | 15 - 30 days Over 86°F |
Annual Climate Data for ZIP Code 51537 - Harlan, IA | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg Min Temp (°F) | 8 | 14 | 25 | 36 | 49 | 59 | 63 | 61 | 51 | 39 | 25 | 14 | 37 |
| Avg Max Temp (°F) | 29 | 35 | 47 | 61 | 72 | 82 | 85 | 82 | 75 | 63 | 46 | 32 | 59 |
| Avg Precip (In.) | .79 | .79 | 2.18 | 3.28 | 4.25 | 4.39 | 4.12 | 3.75 | 4.32 | 2.64 | 1.81 | 1.01 | 33.33 |