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 99505
The USDA's 2023 Plant Hardiness Zone Map puts ZIP 99505 in zone 5a (the coldest night of a typical year: -20 to -15°F).
The nearest station, Fort Richardson Water Treatment Plant, AK, is 4 miles from the ZIP's center: its last spring frost comes after May 9 in half of years and after May 22 in one year in ten. By the USDA's method its plant hardiness zone is 5a.
| Station | Distance | Elevation | Last frost (median) | 1 in 10 after | First frost (median) | Hardiness zone |
|---|---|---|---|---|---|---|
| Fort Richardson Water Treatment Plant, AK | 4 mi | 470 ft | May 9 | May 22 | September 26 | 5a |
| Eagle River Gakona Circle, AK | 4 mi | 567 ft | May 9 | May 22 | September 26 | 5b |
| Eagle River (5 mi SE), AK | 7 mi | 498 ft | May 21 | June 3 | September 15 | 4b |
| Anchorage Merrill Field, AK | 8 mi | 138 ft | May 1 | May 9 | September 29 | 5b |
| Campbell Creek Science Center, AK | 9 mi | 258 ft | May 28 | June 6 | September 12 | – |
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 Fort Richardson Water Treatment Plant
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 30 | May 25 | May 12 | September 14 | August 29 |
| 32°F | May 22 | May 14 | May 9 | April 28 | September 26 | September 9 |
| 28°F (hard freeze) | May 9 | May 2 | April 28 | April 13 | October 6 | September 22 |
| 24°F | April 30 | April 22 | April 16 | April 5 | October 16 | October 1 |
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.