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 46409
The USDA's 2023 Plant Hardiness Zone Map puts ZIP 46409 in zone 6a (the coldest night of a typical year: -10 to -5°F).
The nearest station, Indiana Dunes National Lakeshore, IN, is 13 miles from the ZIP's center: its last spring frost comes after April 22 in half of years and after May 8 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 |
|---|---|---|---|---|---|---|
| Indiana Dunes National Lakeshore, IN | 13 mi | 680 ft | April 22 | May 8 | October 27 | 6a |
| Valparaiso Water Works, IN | 15 mi | 800 ft | April 22 | May 6 | October 25 | – |
| Valparaiso, INValparaiso Porter County Municipal Airport | 18 mi | 770 ft | April 20 | May 7 | October 26 | 6a |
| Park Forest, IL | 19 mi | 710 ft | April 23 | May 11 | October 20 | 6a |
| Lowell, IN | 20 mi | 665 ft | April 29 | May 14 | October 16 | 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 Indiana Dunes National Lakeshore
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 11 | May 4 | April 20 | October 16 | October 4 |
| 32°F | May 8 | April 29 | April 22 | April 7 | October 27 | October 15 |
| 28°F (hard freeze) | April 23 | April 14 | April 8 | March 26 | November 7 | October 26 |
| 24°F | April 12 | April 3 | March 29 | March 12 | November 19 | November 4 |
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.