Frost dates for Thorne Bay, AK
At Thorne Bay, the median last spring frost (32°F) is May 1 and the median first fall frost is Oct 13, for a typical growing season of 166 days. For a 90% chance that the last frost has passed, wait until May 16. Nearby ZIP codes are in USDA hardiness zones 7b to 8a.
- May 1Last spring frost (median)50% chance of 32°F after this date
- May 16Safer planting date10% chance of 32°F after this date
- Oct 13First fall frost (median)50% chance of 32°F by this date
- 166 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 2 | May 17 | Jun 1 |
| 32°F | Apr 17 | May 1 | May 16 |
| 28°F | Mar 26 | Apr 11 | Apr 25 |
| 24°F | Mar 3 | Mar 20 | Apr 6 |
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 18 | Oct 1 | Oct 13 |
| 32°F | Oct 1 | Oct 13 | Oct 28 |
| 28°F | Oct 12 | Oct 30 | Nov 19 |
| 24°F | Oct 27 | Nov 20 | Dec 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 | 118 days | 136 days | 155 days |
| 32°F | 148 days | 166 days | 186 days |
| 28°F | 180 days | 202 days | 227 days |
| 24°F | 211 days | 241 days | 277 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 |
|---|---|---|---|
| 99919 | 7b | 5 to 10°F | 5 km |
| 99921 | 7b | 5 to 10°F | 23 km |
| 99903 | 7b | 5 to 10°F | 27 km |
| 99918 | 8a | 10 to 15°F | 27 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 USC00509148, at 55.6917, -132.5247, elevation 87 m (286 ft).
- Data quality: Estimated from nearby stations (2+ years), 7 years of freeze data.
- Average days per year at or below 32°F: 118.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Klawock Airport (37 km)
- Craig (45 km)
- Ketchikan 10n (52 km)
- Ketchikan Intl Airport (63 km)
- Beaver Falls (64 km)
- Wrangell Airport (87 km)
- Metlakatla 6 S (93 km)
- Annette Island Airport (94 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.