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 99540
The USDA's 2023 Plant Hardiness Zone Map puts ZIP 99540 in zone 5b (the coldest night of a typical year: -15 to -10°F).
The nearest station, Alyeska, AK, is 8 miles from the ZIP's center: its last spring frost comes after May 8 in half of years and after May 22 in one year in ten. By the USDA's method its plant hardiness zone is 6a.
| Station | Distance | Elevation | Last frost (median) | 1 in 10 after | First frost (median) | Hardiness zone |
|---|---|---|---|---|---|---|
| Alyeska, AK | 8 mi | 272 ft | May 8 | May 22 | September 29 | 6a |
| Hope, AK | 13 mi | 180 ft | May 18 | May 28 | September 24 | – |
| Glen Alps, AK | 14 mi | 2,202 ft | May 18 | May 31 | September 23 | 5b |
| Anchorage Upper De Armoun, AK | 15 mi | 1,335 ft | May 7 | May 23 | September 28 | – |
| Eagle River Nature Center, AK | 16 mi | 520 ft | May 16 | June 9 | September 20 | – |
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 Alyeska
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) | June 5 | May 29 | May 24 | May 12 | September 17 | September 1 |
| 32°F | May 22 | May 14 | May 8 | April 26 | September 29 | September 14 |
| 28°F (hard freeze) | May 7 | May 1 | April 26 | April 12 | October 11 | September 27 |
| 24°F | April 28 | April 18 | April 12 | March 31 | October 21 | October 5 |
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.