Frost dates for Casper Natrona Co Airport, WY
At Casper Natrona Co Airport, the median last spring frost (32°F) is May 26 and the median first fall frost is Sep 22, for a typical growing season of 117 days. For a 90% chance that the last frost has passed, wait until Jun 10. Nearby ZIP codes are in USDA hardiness zone 5a.
- May 26Last spring frost (median)50% chance of 32°F after this date
- Jun 10Safer planting date10% chance of 32°F after this date
- Sep 22First fall frost (median)50% chance of 32°F by this date
- 117 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 25 | Jun 9 | Jun 25 |
| 32°F | May 12 | May 26 | Jun 10 |
| 28°F | Apr 30 | May 11 | May 27 |
| 24°F | Apr 16 | Apr 30 | May 14 |
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 26 | Sep 9 | Sep 24 |
| 32°F | Sep 5 | Sep 22 | Oct 4 |
| 28°F | Sep 17 | Oct 2 | Oct 15 |
| 24°F | Oct 1 | Oct 13 | 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 | 69 days | 92 days | 112 days |
| 32°F | 96 days | 117 days | 136 days |
| 28°F | 120 days | 141 days | 161 days |
| 24°F | 146 days | 165 days | 183 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 |
|---|---|---|---|
| 82604 | 5a | -20 to -15°F | 20 km |
| 82601 | 5a | -20 to -15°F | 22 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 USW00024089, at 42.8975, -106.4636, elevation 1627 m (5,338 ft).
- Data quality: Standard (24+ years of data), 29 years of freeze data.
- Average days per year at or below 32°F: 183.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Casper Wastewater Plant (15 km)
- Casper 1sw (15 km)
- Bates Creek #2 (32 km)
- Powder River #2 (45 km)
- Powder River (school) (45 km)
- Pathfinder Dam (57 km)
- Midwest (59 km)
- Shirley Basin (66 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.