Frost dates in USDA zone 1a (-60 to -55°F)
USDA zone 1a covers places whose coldest winter night averages -60 to -55°F. Only 1 NOAA weather station is matched to ZIP codes in zone 1a, and 1 has frost dates: too few stations for a zone-wide median. Each station’s own dates are listed below. Missing dates here mean incomplete records, not a lack of frost. Enter your ZIP for your local date.
- 5ZIP codes in zone 1a-60 to -55°F average coldest night
- 1Stations with frost datesof 1 NOAA stations matched
Every NOAA station in zone 1a
| Station | Last spring frost | First fall frost |
|---|---|---|
| Central #2, AK | May 25 | Aug 26 |
Zone 1a by state
| State | Stations | With frost dates |
|---|---|---|
| Alaska | 1 | 1 |
Neighboring zones
- Zone 1b (-55 to -50°F): too few stations for a median
How these numbers are made
Each ZIP code gets one zone from the USDA-ARS / PRISM 2023 ZIP tables, which use the map’s 1991–2020 average of the coldest winter night of each year. A ZIP code can span more than one zone, and USDA’s own lookup works by ZIP or address. Each NOAA station is assigned the most common zone among the closest ZIP codes listed on its station page (a tie goes to the zone of the closest of those ZIPs). Frost dates are NOAA’s 50%-probability (median) 32°F dates for each station, the same values shown on the station pages. Zone figures are the median, 10th and 90th percentile across stations; a first fall frost in January to June is counted in the following year.
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.
Sources
- 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.
- 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.
- 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.