Frost dates for Keystone Ridge, AK
At Keystone Ridge, the median last spring frost (32°F) is May 15 and the median first fall frost is Sep 16, for a typical growing season of 122 days. For a 90% chance that the last frost has passed, wait until May 31. Nearby ZIP codes are in USDA hardiness zones 2a to 3b.
- May 15Last spring frost (median)50% chance of 32°F after this date
- May 31Safer planting date10% chance of 32°F after this date
- Sep 16First fall frost (median)50% chance of 32°F by this date
- 122 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 12 | May 28 | Jun 20 |
| 32°F | May 3 | May 15 | May 31 |
| 28°F | Apr 23 | May 7 | May 22 |
| 24°F | Apr 14 | Apr 30 | May 13 |
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 17 | Sep 3 | Sep 18 |
| 32°F | Aug 30 | Sep 16 | Sep 28 |
| 28°F | Sep 10 | Sep 25 | Oct 7 |
| 24°F | Sep 19 | Oct 3 | Oct 16 |
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 | 70 days | 98 days | 120 days |
| 32°F | 99 days | 122 days | 140 days |
| 28°F | 120 days | 140 days | 159 days |
| 24°F | 137 days | 156 days | 174 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 |
|---|---|---|---|
| 99709 | 3b | -35 to -30°F | 7 km |
| 99725 | 3b | -35 to -30°F | 13 km |
| 99775 | 2b | -45 to -40°F | 22 km |
| 99703 | 2a | -50 to -45°F | 32 km |
| 99705 | 2a | -50 to -45°F | 50 km |
| 99758 | 2a | -50 to -45°F | 58 km |
| 99790 | 3b | -35 to -30°F | 61 km |
| 99702 | 2a | -50 to -45°F | 65 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 USC00504621, at 64.9156, -148.2711, elevation 488 m (1,600 ft).
- Data quality: Representative (10+ years), 24 years of freeze data.
- Average days per year at or below 32°F: 214.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Ester (14 km)
- Ester 5ne (16 km)
- College 5 NW (18 km)
- Goldstream Creek (19 km)
- University Exp. Station (20 km)
- College Obsy (21 km)
- Fairbanks Airport #2 (22 km)
- Fairbanks Intl Airport (22 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.