Frost dates for Powder River (school), WY
At Powder River (school), the median last spring frost (32°F) is May 30 and the median first fall frost is Sep 22, for a typical growing season of 115 days. For a 90% chance that the last frost has passed, wait until Jun 13. Nearby ZIP codes are in USDA hardiness zone 5a.
- May 30Last spring frost (median)50% chance of 32°F after this date
- Jun 13Safer planting date10% chance of 32°F after this date
- Sep 22First fall frost (median)50% chance of 32°F by this date
- 115 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 26 | Jun 11 | Jun 25 |
| 32°F | May 12 | May 30 | Jun 13 |
| 28°F | Apr 29 | May 12 | May 29 |
| 24°F | Apr 12 | Apr 30 | May 11 |
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 | Aug 31 | Sep 13 | Sep 26 |
| 32°F | Sep 8 | Sep 22 | Oct 4 |
| 28°F | Sep 16 | Oct 1 | Oct 15 |
| 24°F | Sep 26 | Oct 11 | Oct 25 |
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 | 70 days | 91 days | 112 days |
| 32°F | 95 days | 115 days | 135 days |
| 28°F | 119 days | 141 days | 162 days |
| 24°F | 144 days | 165 days | 187 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 |
|---|---|---|---|
| 82638 | 5a | -20 to -15°F | 22 km |
| 82630 | 5a | -20 to -15°F | 42 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 USC00487375, at 43.0353, -106.9894, elevation 1744 m (5,722 ft).
- Data quality: Representative (10+ years), 11 years of freeze data.
- Average days per year at or below 32°F: 200.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Powder River #2 (0 km)
- Casper Natrona Co Airport (45 km)
- Casper Wastewater Plant (60 km)
- Casper 1sw (61 km)
- Pathfinder Dam (64 km)
- Bates Creek #2 (69 km)
- Midwest (71 km)
- Kaycee (81 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.