Frost dates for Arrowrock Dam, ID
At Arrowrock Dam, the median last spring frost (32°F) is Apr 28 and the median first fall frost is Oct 14, for a typical growing season of 169 days. For a 90% chance that the last frost has passed, wait until May 16. Nearby ZIP codes are in USDA hardiness zone 7a.
- Apr 28Last spring frost (median)50% chance of 32°F after this date
- May 16Safer planting date10% chance of 32°F after this date
- Oct 14First fall frost (median)50% chance of 32°F by this date
- 169 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 | Apr 30 | May 16 | Jun 8 |
| 32°F | Apr 11 | Apr 28 | May 16 |
| 28°F | Mar 13 | Apr 6 | Apr 30 |
| 24°F | Feb 25 | Mar 12 | Apr 4 |
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 21 | Oct 4 | Oct 16 |
| 32°F | Oct 1 | Oct 14 | Oct 29 |
| 28°F | Oct 12 | Oct 27 | Nov 15 |
| 24°F | Oct 21 | Nov 10 | Nov 26 |
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 | 111 days | 139 days | 163 days |
| 32°F | 143 days | 169 days | 192 days |
| 28°F | 171 days | 203 days | 231 days |
| 24°F | 207 days | 239 days | 266 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 |
|---|---|---|---|
| 83712 | 7a | 0 to 5°F | 14 km |
| 83702 | 7a | 0 to 5°F | 19 km |
| 83706 | 7a | 0 to 5°F | 22 km |
| 83720 | 7a | 0 to 5°F | 22 km |
| 83705 | 7a | 0 to 5°F | 24 km |
| 83703 | 7a | 0 to 5°F | 27 km |
| 83704 | 7a | 0 to 5°F | 30 km |
| 83709 | 7a | 0 to 5°F | 30 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 USC00100448, at 43.5936, -115.9236, elevation 986 m (3,235 ft).
- Data quality: Representative (10+ years), 14 years of freeze data.
- Average days per year at or below 32°F: 134.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Boise Lucky Peak Dam (13 km)
- Boise Air Terminal (26 km)
- Boise 7 N (28 km)
- Idaho City (28 km)
- Emmett 2 E (52 km)
- Nampa Sugar Factory (52 km)
- Swan Falls Ph (54 km)
- Mountain Home (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.