Frost dates by ZIP code: The nearest NOAA stations to your ZIP, 1991-2020 normals
Enter a five-digit ZIP code. PlainClimate finds its center (Census Bureau 2024) and the five nearest NOAA stations with frost dates, and shows each station's last spring and first autumn 32°F dates with its distance and elevation.
Frost dates near ZIP 99508
The USDA's 2023 Plant Hardiness Zone Map puts ZIP 99508 in zone 5a (the coldest night of a typical year: -20 to -15°F).
The nearest station, Anchorage Merrill Field, AK, is 2 miles from the ZIP's center: its last spring frost comes after May 1 in half of years and after May 9 in one year in ten. By the USDA's method its plant hardiness zone is 5b.
| Station | Distance | Elevation | Last frost (median) | 1 in 10 after | First frost (median) | Hardiness zone |
|---|---|---|---|---|---|---|
| Anchorage Merrill Field, AK | 2 mi | 138 ft | May 1 | May 9 | September 29 | 5b |
| Campbell Creek Science Center, AK | 3 mi | 258 ft | May 28 | June 6 | September 12 | – |
| Anchorage Lake Hood Airport, AK | 5 mi | 90 ft | May 1 | May 8 | October 3 | 5b |
| Fort Richardson Water Treatment Plant, AK | 6 mi | 470 ft | May 9 | May 22 | September 26 | 5a |
| Anchorage Forecast Office, AK | 6 mi | 131 ft | May 5 | May 14 | September 29 | 5b |
Frost comes later in spring at higher and colder stations and earlier in low, open ground: prefer a station at a similar elevation to yours. Hardiness zone in the table: the USDA's rule (the average of each year's coldest night, 1991-2020) applied to the station's own record.
Every frost threshold at Anchorage Merrill Field
NOAA publishes the dates for several temperatures and odds. A 30% spring date means a 3-in-10 chance of a later frost (the convention almanacs use); 50% is the median; 10% the cautious date.
| Threshold | Spring, 10% | Spring, 30% | Spring, 50% | Spring, 90% | Autumn, 50% | Autumn, 10% |
|---|---|---|---|---|---|---|
| 36°F (light frost) | May 23 | May 16 | May 12 | May 2 | September 20 | September 7 |
| 32°F | May 9 | May 4 | May 1 | April 19 | September 29 | September 17 |
| 28°F (hard freeze) | May 1 | April 24 | April 19 | April 10 | October 8 | September 27 |
| 24°F | April 24 | April 15 | April 10 | April 1 | October 18 | October 3 |
Source: NOAA NCEI 1991-2020 annual normals; ZIP centers: Census Bureau 2024 Gazetteer; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026. Autumn 10%: one year in ten has its first frost before this date.