Frost dates for Casper 1sw, WY
At Casper 1sw, the median last spring frost (32°F) is May 12 and the median first fall frost is Oct 1, for a typical growing season of 143 days. For a 90% chance that the last frost has passed, wait until May 26. Nearby ZIP codes are in USDA hardiness zone 5a.
- May 12Last spring frost (median)50% chance of 32°F after this date
- May 26Safer planting date10% chance of 32°F after this date
- Oct 1First fall frost (median)50% chance of 32°F by this date
- 143 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 11 | May 24 | Jun 5 |
| 32°F | Apr 28 | May 12 | May 26 |
| 28°F | Apr 13 | Apr 30 | May 14 |
| 24°F | Mar 29 | Apr 15 | May 1 |
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 10 | Sep 23 | Oct 6 |
| 32°F | Sep 18 | Oct 1 | Oct 19 |
| 28°F | Sep 27 | Oct 13 | Oct 28 |
| 24°F | Oct 5 | Oct 22 | Nov 8 |
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 | 104 days | 122 days | 141 days |
| 32°F | 123 days | 143 days | 163 days |
| 28°F | 142 days | 165 days | 186 days |
| 24°F | 164 days | 188 days | 212 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 |
|---|---|---|---|
| 82636 | 5a | -20 to -15°F | 11 km |
| 82609 | 5a | -20 to -15°F | 12 km |
| 82637 | 5a | -20 to -15°F | 36 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 USC00481572, at 42.8519, -106.2844, elevation 1568 m (5,143 ft).
- Data quality: Estimated from nearby stations (2+ years), 5 years of freeze data.
- Average days per year at or below 32°F: 156.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Casper Wastewater Plant (1 km)
- Casper Natrona Co Airport (15 km)
- Bates Creek #2 (26 km)
- Shirley Basin (56 km)
- Powder River #2 (61 km)
- Powder River (school) (61 km)
- Midwest (62 km)
- Pathfinder Dam (63 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.