Frost dates for Black Mountain, WY
At Black Mountain, the median last spring frost (32°F) is May 14 and the median first fall frost is Oct 3, for a typical growing season of 140 days. For a 90% chance that the last frost has passed, wait until Jun 1. Nearby ZIP codes are in USDA hardiness zones 4b to 5a.
- May 14Last spring frost (median)50% chance of 32°F after this date
- Jun 1Safer planting date10% chance of 32°F after this date
- Oct 3First fall frost (median)50% chance of 32°F by this date
- 140 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 27 | Jun 11 |
| 32°F | Apr 29 | May 14 | Jun 1 |
| 28°F | Apr 15 | May 1 | May 19 |
| 24°F | Mar 30 | Apr 18 | May 6 |
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 25 | Oct 9 |
| 32°F | Sep 20 | Oct 3 | Oct 18 |
| 28°F | Sep 28 | Oct 12 | Oct 28 |
| 24°F | Oct 4 | Oct 20 | 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 | 99 days | 120 days | 141 days |
| 32°F | 119 days | 140 days | 163 days |
| 28°F | 140 days | 162 days | 185 days |
| 24°F | 160 days | 185 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% |
Closest ZIP codes (each is closer to another station)
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 82430 | 4b | -25 to -20°F | 39 km |
| 82642 | 5a | -20 to -15°F | 42 km |
| 82442 | 5a | -20 to -15°F | 43 km |
| 82649 | 4b | -25 to -20°F | 47 km |
| 82630 | 5a | -20 to -15°F | 50 km |
| 82401 | 4b | -25 to -20°F | 53 km |
| 82443 | 5a | -20 to -15°F | 60 km |
| 82432 | 4b | -25 to -20°F | 63 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 USC00480778, at 43.6561, -107.7375, elevation 1718 m (5,635 ft).
- Data quality: Representative (10+ years), 20 years of freeze data.
- Average days per year at or below 32°F: 164.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Thermopolis 9ne (34 km)
- Tensleep 16sse (35 km)
- Thermopolis (38 km)
- Worland (38 km)
- Worland (44 km)
- Boysen Dam (44 km)
- Tensleep 4ne (54 km)
- Shoshoni (55 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.