Frost dates for Chilly Barton Flat, ID
At Chilly Barton Flat, the median last spring frost (32°F) is Jun 14 and the median first fall frost is Sep 8, for a typical growing season of 86 days. For a 90% chance that the last frost has passed, wait until Jun 30. Nearby ZIP codes are in USDA hardiness zone 5a.
- Jun 14Last spring frost (median)50% chance of 32°F after this date
- Jun 30Safer planting date10% chance of 32°F after this date
- Sep 8First fall frost (median)50% chance of 32°F by this date
- 86 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 |
|---|---|---|---|
| 32°F | May 27 | Jun 14 | Jun 30 |
| 28°F | May 7 | May 24 | Jun 15 |
| 24°F | Apr 21 | May 7 | May 27 |
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 |
|---|---|---|---|
| 32°F | Aug 26 | Sep 8 | Sep 22 |
| 28°F | Sep 5 | Sep 20 | Oct 4 |
| 24°F | Sep 16 | Oct 1 | Oct 19 |
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 | 37 days | 60 days | 80 days |
| 32°F | 65 days | 86 days | 109 days |
| 28°F | 92 days | 118 days | 140 days |
| 24°F | 123 days | 146 days | 168 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 |
|---|---|---|---|
| 83251 | 5a | -20 to -15°F | 10 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 USC00101671, at 43.9778, -113.8292, elevation 1908 m (6,260 ft).
- Data quality: Standard (24+ years of data), 28 years of freeze data.
- Average days per year at or below 32°F: 217.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Mackay Lost River Ranger Station (18 km)
- Ketchum Ranger Station (54 km)
- Arco (57 km)
- Craters Of The Moon (61 km)
- Arco 17 SW (61 km)
- May 2sse (66 km)
- Bellevue (66 km)
- Challis Airport (68 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.