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 99903
The USDA's 2023 Plant Hardiness Zone Map puts ZIP 99903 in zone 7b (the coldest night of a typical year: 5 to 10°F).
The nearest station, Thorne Bay, AK, is 17 miles from the ZIP's center: its last spring frost comes after May 1 in half of years and after May 16 in one year in ten.
| Station | Distance | Elevation | Last frost (median) | 1 in 10 after | First frost (median) | Hardiness zone |
|---|---|---|---|---|---|---|
| Thorne Bay, AK | 17 mi | 286 ft | May 1 | May 16 | October 13 | – |
| Ketchikan (10 mi N), AK | 22 mi | 295 ft | April 20 | May 4 | October 26 | – |
| Ketchikan, AKKetchikan International Airport | 30 mi | 76 ft | April 22 | May 9 | October 23 | 7b |
| Beaver Falls, AK | 30 mi | 35 ft | April 4 | April 25 | November 9 | – |
| Klawock, AKKlawock Airport | 39 mi | 12 ft | April 29 | May 14 | October 16 | 8a |
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 Thorne Bay
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 1 | May 23 | May 17 | May 2 | October 1 | September 18 |
| 32°F | May 16 | May 5 | May 1 | April 17 | October 13 | October 1 |
| 28°F (hard freeze) | April 25 | April 16 | April 11 | March 26 | October 30 | October 12 |
| 24°F | April 6 | March 27 | March 20 | March 3 | November 20 | October 27 |
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.