Frost dates for Arco, ID
At Arco, the median last spring frost (32°F) is May 22 and the median first fall frost is Sep 22, for a typical growing season of 119 days. For a 90% chance that the last frost has passed, wait until Jun 9. Nearby ZIP codes are in USDA hardiness zone 5a.
- May 22Last spring frost (median)50% chance of 32°F after this date
- Jun 9Safer planting date10% chance of 32°F after this date
- Sep 22First fall frost (median)50% chance of 32°F by this date
- 119 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 22 | Jun 7 | Jun 28 |
| 32°F | May 5 | May 22 | Jun 9 |
| 28°F | Apr 20 | May 6 | May 24 |
| 24°F | Apr 6 | Apr 23 | May 8 |
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 25 | Sep 10 | Sep 26 |
| 32°F | Sep 4 | Sep 22 | Oct 7 |
| 28°F | Sep 16 | Oct 3 | Oct 19 |
| 24°F | Sep 28 | Oct 16 | Oct 30 |
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 | 65 days | 92 days | 117 days |
| 32°F | 92 days | 119 days | 142 days |
| 28°F | 124 days | 146 days | 169 days |
| 24°F | 151 days | 175 days | 200 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 |
|---|---|---|---|
| 83255 | 5a | -20 to -15°F | 15 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 USC00100375, at 43.6356, -113.2997, elevation 1623 m (5,325 ft).
- Data quality: Representative (10+ years), 26 years of freeze data.
- Average days per year at or below 32°F: 192.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Arco 17 SW (28 km)
- Craters Of The Moon (28 km)
- Howe (29 km)
- Idaho Falls 46 W (31 km)
- Mackay Lost River Ranger Station (40 km)
- Chilly Barton Flat (57 km)
- Picabo (72 km)
- Monteview (73 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.