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 62521
The USDA's 2023 Plant Hardiness Zone Map puts ZIP 62521 in zone 6a (the coldest night of a typical year: -10 to -5°F).
The nearest station, Decatur Water Treatment Plant, IL, is 2 miles from the ZIP's center: its last spring frost comes after April 14 in half of years and after May 1 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 |
|---|---|---|---|---|---|---|
| Decatur Water Treatment Plant, IL | 2 mi | 639 ft | April 14 | May 1 | October 24 | 6a |
| Decatur, ILDecatur Airport | 4 mi | 675 ft | April 16 | April 30 | October 22 | 6b |
| Sullivan, IL3 mi S | 24 mi | 640 ft | April 15 | April 30 | October 22 | – |
| Shelbyville, ILShelbyville Dam | 29 mi | 650 ft | April 10 | April 28 | October 24 | 6b |
| Windsor, IL | 31 mi | 690 ft | April 16 | April 30 | October 22 | 6b |
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 Decatur 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) | May 13 | May 3 | April 26 | April 12 | October 14 | September 30 |
| 32°F | May 1 | April 20 | April 14 | April 1 | October 24 | October 11 |
| 28°F (hard freeze) | April 17 | April 7 | April 3 | March 18 | November 3 | October 20 |
| 24°F | April 7 | March 31 | March 24 | March 7 | November 12 | October 30 |
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.