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 80304
The USDA's 2023 Plant Hardiness Zone Map puts ZIP 80304 in zone 6a (the coldest night of a typical year: -10 to -5°F).
The nearest station, Boulder, CO, is 4 miles from the ZIP's center: its last spring frost comes after May 6 in half of years and after May 18 in one year in ten.
| Station | Distance | Elevation | Last frost (median) | 1 in 10 after | First frost (median) | Hardiness zone |
|---|---|---|---|---|---|---|
| Boulder, CO | 4 mi | 5,484 ft | May 6 | May 18 | October 5 | – |
| Gross Reservoir, CO | 8 mi | 7,970 ft | May 24 | June 10 | September 23 | 5b |
| Coal Creek, COCoal Creek Canyon | 11 mi | 8,950 ft | June 5 | June 19 | September 16 | 5b |
| Boulder (14 mi W), CO | 13 mi | 9,828 ft | June 21 | July 4 | September 2 | 5a |
| Longmont, CO2 mi ESE | 14 mi | 4,950 ft | May 7 | May 22 | October 5 | – |
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 Boulder
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 2 | May 22 | May 17 | May 5 | September 28 | September 13 |
| 32°F | May 18 | May 11 | May 6 | April 24 | October 5 | September 21 |
| 28°F (hard freeze) | May 10 | May 2 | April 27 | April 10 | October 15 | September 30 |
| 24°F | May 2 | April 22 | April 14 | March 29 | October 25 | October 7 |
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.