Frost dates for Mackay Lost River Ranger Station, ID
At Mackay Lost River Ranger Station, the median last spring frost (32°F) is Jun 1 and the median first fall frost is Sep 20, for a typical growing season of 109 days. For a 90% chance that the last frost has passed, wait until Jun 21. Nearby ZIP codes are in USDA hardiness zones 5a to 6a.
- Jun 1Last spring frost (median)50% chance of 32°F after this date
- Jun 21Safer planting date10% chance of 32°F after this date
- Sep 20First fall frost (median)50% chance of 32°F by this date
- 109 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 | Jun 1 | Jun 18 | Jul 3 |
| 32°F | May 13 | Jun 1 | Jun 21 |
| 28°F | Apr 30 | May 13 | Jun 4 |
| 24°F | Apr 14 | Apr 30 | May 15 |
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 24 | Sep 6 | Sep 22 |
| 32°F | Sep 4 | Sep 20 | Oct 3 |
| 28°F | Sep 16 | Oct 1 | Oct 15 |
| 24°F | Sep 28 | Oct 13 | Oct 28 |
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 | 57 days | 80 days | 102 days |
| 32°F | 87 days | 109 days | 130 days |
| 28°F | 113 days | 138 days | 159 days |
| 24°F | 144 days | 166 days | 188 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 |
|---|---|---|---|
| 83255 | 5a | -20 to -15°F | 26 km |
| 83251 | 5a | -20 to -15°F | 27 km |
| 83244 | 5a | -20 to -15°F | 53 km |
| 83213 | 5a | -20 to -15°F | 56 km |
| 83226 | 5b | -15 to -10°F | 60 km |
| 83320 | 6a | -10 to -5°F | 61 km |
| 83353 | 5b | -15 to -10°F | 62 km |
| 83354 | 5b | -15 to -10°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 USC00105462, at 43.9178, -113.6153, elevation 1797 m (5,897 ft).
- Data quality: Standard (24+ years of data), 27 years of freeze data.
- Average days per year at or below 32°F: 202.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Chilly Barton Flat (18 km)
- Arco (40 km)
- Craters Of The Moon (51 km)
- Arco 17 SW (51 km)
- Howe (51 km)
- Ketchum Ranger Station (65 km)
- Idaho Falls 46 W (69 km)
- Bellevue (72 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.