Frost dates for Port San Juan, AK
At Port San Juan, the median last spring frost (32°F) is May 10 and the median first fall frost is Oct 7, for a typical growing season of 150 days. For a 90% chance that the last frost has passed, wait until May 28. Nearby ZIP codes are in USDA hardiness zones 5a to 8a.
- May 10Last spring frost (median)50% chance of 32°F after this date
- May 28Safer planting date10% chance of 32°F after this date
- Oct 7First fall frost (median)50% chance of 32°F by this date
- 150 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 15 | May 31 | Jun 20 |
| 32°F | Apr 26 | May 10 | May 28 |
| 28°F | Apr 5 | Apr 23 | May 7 |
| 24°F | Mar 18 | Apr 5 | Apr 25 |
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 7 | Sep 24 | Oct 6 |
| 32°F | Sep 22 | Oct 7 | Oct 27 |
| 28°F | Oct 6 | Oct 25 | Nov 14 |
| 24°F | Oct 26 | Nov 12 | Nov 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 | 92 days | 115 days | 135 days |
| 32°F | 125 days | 150 days | 174 days |
| 28°F | 161 days | 186 days | 211 days |
| 24°F | 195 days | 221 days | 244 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 |
|---|---|---|---|
| 99664 | 5b | -15 to -10°F | 80 km |
| 99693 | 7a | 0 to 5°F | 89 km |
| 99631 | 5a | -20 to -15°F | 106 km |
| 99587 | 5b | -15 to -10°F | 111 km |
| 99572 | 5a | -20 to -15°F | 117 km |
| 99605 | 5b | -15 to -10°F | 119 km |
| 99677 | 8a | 10 to 15°F | 121 km |
| 99574 | 5a | -20 to -15°F | 121 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 USC00507738, at 60.0503, -148.0672, elevation 12 m (40 ft).
- Data quality: Standard (24+ years of data), 28 years of freeze data.
- Average days per year at or below 32°F: 136.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Main Bay (52 km)
- Seward Airport (75 km)
- Seward 19n (78 km)
- Wally Noerenberg Hatchery (83 km)
- Whittier (88 km)
- Seward 8 NW (88 km)
- Moose Pass 3nw (90 km)
- Portage Glacier V C (92 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.