South Dakota frost dates by city
| City | Last frost (50%) | Safer date (10%) | First frost (50%) | Season |
|---|---|---|---|---|
| Rapid City | May 12 | May 26 | Oct 1 | 139 days |
| Sioux Falls | May 1 | May 14 | Oct 6 | 157 days |
Each city uses its nearest major NOAA weather station, usually the airport. Valleys, hilltops and rural spots can differ from it by one to three weeks. How to read these dates.