Frost dates for Watertown Regional Airport, SD
At Watertown Regional Airport, the median last spring frost (32°F) is May 7 and the median first fall frost is Sep 30, for a typical growing season of 145 days. For a 90% chance that the last frost has passed, wait until May 20. Nearby ZIP codes are in USDA hardiness zone 4b.
- May 7Last spring frost (median)50% chance of 32°F after this date
- May 20Safer planting date10% chance of 32°F after this date
- Sep 30First fall frost (median)50% chance of 32°F by this date
- 145 daysGrowing season (median)between 32°F freezes
Last spring frost dates
The chance that the temperature drops to the threshold after each date.
| Temperature | 90% chance later | 50% chance later | 10% chance later |
|---|---|---|---|
| 36°F | May 4 | May 17 | May 31 |
| 32°F | Apr 26 | May 7 | May 20 |
| 28°F | Apr 14 | Apr 29 | May 11 |
| 24°F | Apr 6 | Apr 20 | May 3 |
First fall frost dates
The chance that the temperature has dropped to the threshold by each date.
| Temperature | 10% chance by | 50% chance by | 90% chance by |
|---|---|---|---|
| 36°F | Sep 9 | Sep 23 | Oct 4 |
| 32°F | Sep 19 | Sep 30 | Oct 13 |
| 28°F | Sep 26 | Oct 9 | Oct 22 |
| 24°F | Oct 4 | Oct 20 | Nov 2 |
Growing season length
Days between the last spring and first fall freeze, as the length reached in 9, 5 and 1 out of 10 years.
| Temperature | 9 in 10 years at least | 5 in 10 years at least | 1 in 10 years at least |
|---|---|---|---|
| 36°F | 108 days | 127 days | 145 days |
| 32°F | 127 days | 145 days | 162 days |
| 28°F | 144 days | 164 days | 183 days |
| 24°F | 163 days | 183 days | 203 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
ZIP codes whose closest station is this one
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 57201 | 4b | -25 to -20°F | 6 km |
| 57243 | 4b | -25 to -20°F | 23 km |
Not the official USDA Plant Hardiness Zone Map. Zones shown here are the values published in the USDA-ARS / Oregon State University PRISM Group 2023 ZIP code tables, shown unaltered. For the official interactive map, visit planthardiness.ars.usda.gov.
About this station
- NOAA station ID USW00014946, at 44.9047, -97.1494, elevation 533 m (1,748 ft).
- Data quality: Standard (24+ years of data), 28 years of freeze data.
- Average days per year at or below 32°F: 174.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Watertown 2 S (5 km)
- Rauville 2 W (8 km)
- Castlewood #2 (22 km)
- Castlewood (22 km)
- Clear Lake (40 km)
- Summit 1 W (45 km)
- Clark (46 km)
- Clark No2 (46 km)
Sources
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, annual/seasonal normals by station (version 1.0.1), file dated June 27, 2023; documentation.
- USDA Agricultural Research Service and PRISM Group, Oregon State University, 2023 Plant Hardiness Zone Map ZIP code tables (CONUS, Alaska, Hawaii, Puerto Rico), files dated November 17, 2023. Data © PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed November 1, 2026. Official map: planthardiness.ars.usda.gov.
- U.S. Census Bureau, 2024 Gazetteer ZIP Code Tabulation Areas file, dated August 30, 2024 (ZIP centroids used to find the nearest station).
Freeze dates are 30-year probabilities, not forecasts. Check your local forecast before planting tender plants.