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 84121
The USDA's 2023 Plant Hardiness Zone Map puts ZIP 84121 in zone 6a (the coldest night of a typical year: -10 to -5°F).
The nearest station, Alta, UT, is 3 miles from the ZIP's center: its last spring frost comes after June 11 in half of years and after June 27 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 |
|---|---|---|---|---|---|---|
| Alta, UT | 3 mi | 8,710 ft | June 11 | June 27 | September 18 | 6a |
| Cottonwood Heights, UTCottonwood Weir | 5 mi | 4,986 ft | April 29 | May 30 | October 22 | 7a |
| Mountain Dell Dam, UT | 9 mi | 5,420 ft | May 7 | May 27 | October 14 | 6b |
| Park City, UT | 10 mi | 6,900 ft | May 29 | June 14 | September 25 | – |
| Salt Lake City E Bench, UT | 11 mi | 4,850 ft | April 25 | May 10 | October 18 | – |
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 Alta
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% |
|---|---|---|---|---|---|---|
| 32°F | June 27 | June 18 | June 11 | May 26 | September 18 | September 3 |
| 28°F (hard freeze) | June 18 | June 8 | June 1 | May 14 | September 27 | September 13 |
| 24°F | June 6 | May 26 | May 17 | April 30 | October 5 | September 21 |
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.