Frost dates for Fort Richardson Water Plant, AK
At Fort Richardson Water Plant, the median last spring frost (32°F) is May 9 and the median first fall frost is Sep 26, for a typical growing season of 138 days. For a 90% chance that the last frost has passed, wait until May 22. Nearby ZIP codes are in USDA hardiness zone 5a.
- May 9Last spring frost (median)50% chance of 32°F after this date
- May 22Safer planting date10% chance of 32°F after this date
- Sep 26First fall frost (median)50% chance of 32°F by this date
- 138 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 25 | Jun 5 |
| 32°F | Apr 28 | May 9 | May 22 |
| 28°F | Apr 13 | Apr 28 | May 9 |
| 24°F | Apr 5 | Apr 16 | Apr 30 |
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 29 | Sep 14 | Sep 27 |
| 32°F | Sep 9 | Sep 26 | Oct 10 |
| 28°F | Sep 22 | Oct 6 | Oct 20 |
| 24°F | Oct 1 | Oct 16 | Oct 29 |
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 | 111 days | 129 days |
| 32°F | 119 days | 138 days | 157 days |
| 28°F | 143 days | 162 days | 180 days |
| 24°F | 162 days | 181 days | 198 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 |
|---|---|---|---|
| 99504 | 5a | -20 to -15°F | 5 km |
| 99505 | 5a | -20 to -15°F | 6 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 USC00503163, at 61.2272, -149.6503, elevation 143 m (470 ft).
- Data quality: Standard (24+ years of data), 27 years of freeze data.
- Average days per year at or below 32°F: 198.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Campbell Creek Sci Center (10 km)
- Anchorage Merrill Field (11 km)
- Eagle River Gakona Circle (12 km)
- Eagle River 5 SE (14 km)
- Anchorage Upper De Armoun (14 km)
- Glen Alps (14 km)
- Anchorage Rabbit Creek #2 (16 km)
- Anchorage Lake Hood Airport (18 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.