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 51109
The USDA's 2023 Plant Hardiness Zone Map puts ZIP 51109 in zone 5a (the coldest night of a typical year: -20 to -15°F).
The nearest station, Sioux City Ang, IA, is 16 miles from the ZIP's center: its last spring frost comes after April 29 in half of years and after May 11 in one year in ten. By the USDA's method its plant hardiness zone is 5b.
| Station | Distance | Elevation | Last frost (median) | 1 in 10 after | First frost (median) | Hardiness zone |
|---|---|---|---|---|---|---|
| Sioux City Ang, IA | 16 mi | 1,100 ft | April 29 | May 11 | October 7 | 5b |
| Sioux City, IASioux City Airport | 16 mi | 1,095 ft | April 29 | May 14 | October 5 | 5a |
| Le Mars, IA | 20 mi | 1,195 ft | April 30 | May 12 | October 4 | 5a |
| Vermillion, SD2 mi SE | 25 mi | 1,137 ft | May 3 | May 16 | October 3 | 5a |
| Hawarden, IA | 27 mi | 1,190 ft | May 1 | May 14 | October 4 | 5a |
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 Sioux City Ang
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 21 | May 13 | May 7 | April 25 | September 29 | September 18 |
| 32°F | May 11 | May 4 | April 29 | April 15 | October 7 | September 24 |
| 28°F (hard freeze) | May 2 | April 25 | April 19 | April 5 | October 18 | October 2 |
| 24°F | April 23 | April 15 | April 9 | March 25 | October 27 | October 14 |
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.