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 80521
The USDA's 2023 Plant Hardiness Zone Map puts ZIP 80521 in zone 5b (the coldest night of a typical year: -15 to -10°F).
The nearest station, Fort Collins, CO, is 2 miles from the ZIP's center: its last spring frost comes after May 2 in half of years and after May 14 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 |
|---|---|---|---|---|---|---|
| Fort Collins, CO | 2 mi | 5,004 ft | May 2 | May 14 | October 7 | 6a |
| Fort Collins (4 mi E), CO | 6 mi | 4,920 ft | May 3 | May 15 | October 6 | – |
| Buckhorn Mountain (1 mi E), CO | 9 mi | 7,400 ft | May 21 | June 4 | September 29 | 5b |
| Loveland, CO2 mi N | 11 mi | 5,080 ft | May 10 | May 22 | October 1 | 5b |
| Waterdale, CO | 12 mi | 5,230 ft | May 12 | May 30 | October 1 | 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 Fort Collins
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 26 | May 17 | May 12 | May 1 | September 29 | September 15 |
| 32°F | May 14 | May 7 | May 2 | April 18 | October 7 | September 24 |
| 28°F (hard freeze) | May 5 | April 27 | April 20 | April 5 | October 17 | October 2 |
| 24°F | April 26 | April 14 | April 6 | March 21 | October 26 | October 12 |
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.