Frost dates for Upton, WY
At Upton, the median last spring frost (32°F) is May 20 and the median first fall frost is Sep 23, for a typical growing season of 123 days. For a 90% chance that the last frost has passed, wait until Jun 4. Nearby ZIP codes are in USDA hardiness zone 4b.
- May 20Last spring frost (median)50% chance of 32°F after this date
- Jun 4Safer planting date10% chance of 32°F after this date
- Sep 23First fall frost (median)50% chance of 32°F by this date
- 123 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 19 | Jun 1 | Jun 20 |
| 32°F | May 8 | May 20 | Jun 4 |
| 28°F | Apr 26 | May 9 | May 24 |
| 24°F | Apr 13 | Apr 29 | May 12 |
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 30 | Sep 13 | Sep 26 |
| 32°F | Sep 7 | Sep 23 | Oct 5 |
| 28°F | Sep 16 | Oct 2 | Oct 15 |
| 24°F | Sep 26 | Oct 13 | Oct 24 |
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 | 77 days | 101 days | 121 days |
| 32°F | 100 days | 123 days | 144 days |
| 28°F | 120 days | 145 days | 165 days |
| 24°F | 144 days | 166 days | 186 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 |
|---|---|---|---|
| 82730 | 4b | -25 to -20°F | 10 km |
| 82723 | 4b | -25 to -20°F | 18 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 USC00489205, at 44.0928, -104.6114, elevation 1317 m (4,320 ft).
- Data quality: Standard (24+ years of data), 27 years of freeze data.
- Average days per year at or below 32°F: 182.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Moorcroft 3s (29 km)
- Dillinger (40 km)
- Sundance (41 km)
- Newcastle (43 km)
- Sundance 8 NNW (49 km)
- Rochelle 7ene (53 km)
- Devils Twr #2 (55 km)
- Hulett (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.