Frost dates for Boysen Dam, WY
At Boysen Dam, the median last spring frost (32°F) is May 5 and the median first fall frost is Oct 7, for a typical growing season of 153 days. For a 90% chance that the last frost has passed, wait until May 20. Nearby ZIP codes are in USDA hardiness zones 4b to 5a.
- May 5Last spring frost (median)50% chance of 32°F after this date
- May 20Safer planting date10% chance of 32°F after this date
- Oct 7First fall frost (median)50% chance of 32°F by this date
- 153 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 5 | May 18 | Jun 2 |
| 32°F | Apr 23 | May 5 | May 20 |
| 28°F | Apr 8 | Apr 26 | May 9 |
| 24°F | Mar 26 | Apr 13 | Apr 30 |
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 16 | Sep 28 | Oct 11 |
| 32°F | Sep 24 | Oct 7 | Oct 20 |
| 28°F | Oct 1 | Oct 17 | Oct 30 |
| 24°F | Oct 12 | Oct 27 | Nov 9 |
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 | 110 days | 131 days | 150 days |
| 32°F | 132 days | 153 days | 171 days |
| 28°F | 153 days | 174 days | 196 days |
| 24°F | 175 days | 196 days | 219 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
Closest ZIP codes (each is closer to another station)
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 82649 | 4b | -25 to -20°F | 19 km |
| 82501 | 5a | -20 to -15°F | 42 km |
| 82443 | 5a | -20 to -15°F | 43 km |
| 82642 | 5a | -20 to -15°F | 43 km |
| 82430 | 4b | -25 to -20°F | 44 km |
| 82523 | 5a | -20 to -15°F | 56 km |
| 82510 | 5a | -20 to -15°F | 58 km |
| 82516 | 5a | -20 to -15°F | 58 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 USC00481000, at 43.4053, -108.1633, elevation 1486 m (4,875 ft).
- Data quality: Representative (10+ years), 24 years of freeze data.
- Average days per year at or below 32°F: 172.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Shoshoni (19 km)
- Thermopolis (27 km)
- Thermopolis 9ne (39 km)
- Black Mountain (44 km)
- Riverton (45 km)
- Riverton (45 km)
- Pavillion (46 km)
- Thermopolis 21wnw (56 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.