Frost dates in Anchorage, Alaska
NOAA 1991–2020 normals for a 32 °F freeze. Low spots and the edge of town run colder than downtown.
Short answer
The average last spring frost in Anchorage is May 1, and the average first fall frost is September 29, from NOAA's Anchorage Merrill Fld station, under a mile from the middle of Anchorage. 1 year in 10 the last frost comes after May 9, and the first one by September 17. That leaves about 151 frost-free days. Anchorage is in USDA planting zone 5a.
Weather stations around Anchorage
The first row is the date most people in Anchorage go by. The others show how far the dates move across the area.
| Station | Last spring frost | First fall frost | Frost-free |
|---|---|---|---|
| Anchorage Merrill Fld Under a mile away, 138 ft | May 1 1 in 10 after May 9 | September 29 1 in 10 by September 17 | 151 days |
| Anchorage Lake Hood Airport 5 mi away, 90 ft | May 1 1 in 10 after May 8 | October 3 1 in 10 by September 22 | 155 days |
| Campbell Creek Sci Ctr 5 mi away, 258 ft | May 28 1 in 10 after June 6 | September 12 1 in 10 by August 30 | 107 days |
| Anchorage Forecast Office 6 mi away, 131 ft | May 5 1 in 10 after May 14 | September 29 1 in 10 by September 17 | 147 days |
| Anchorage Intl Airport 7 mi away, 120 ft | May 5 1 in 10 after May 15 | October 1 1 in 10 by September 18 | 149 days |
Distances are from the middle of Anchorage as the Census Bureau maps it. The average date is NOAA's 50% date: half of years have a later last frost, or an earlier first one. Plan by the 1-in-10 date if a freeze would cost you plants. The planting zone is the USDA 2023 zone for ZIP code 99501, at the middle of the city.
Your exact ZIP code
Anchorage covers a lot of ground. For the station nearest your own street, and its planting zone, type your ZIP code.
How these dates work
Frost dates come from NOAA's 1991 to 2020 Climate Normals, which work out from each weather station's daily lows how likely the last spring freeze and the first fall freeze (32 °F) are by each date. We use the station nearest the middle of your ZIP code and show its height and distance, since a station on a hill or by a lake can differ from your yard.
The average date is the 50% date: half of years have a freeze after the spring date or before the fall one. The 1-in-10 dates are NOAA's 10% dates, the ones to plan by if a late freeze would cost you plants. Within one yard, cold air pools in low spots while walls and paving hold heat, so some corners freeze before others.
More frost dates
All of Alaska, station by station.
Nearby: Seattle, WA · Bellevue, WA · Tacoma, WA
Where the numbers come from
- USDA Plant Hardiness Zone Map, 2023. Agricultural Research Service, U.S. Department of Agriculture
- PRISM Climate Group, Oregon State University (zone data)
- NOAA NCEI, U.S. Climate Normals 1991–2020, annual/seasonal
- NOAA, Normals calculation methodology (frost-freeze probability dates)
- US Census Bureau, 2025 ZCTA gazetteer (ZIP code centers)
- US Census Bureau, 2025 city population estimates and place gazetteer