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 91791
The USDA's 2023 Plant Hardiness Zone Map puts ZIP 91791 in zone 10a (the coldest night of a typical year: 30 to 35°F).
The nearest station, Pomona, CA, is 7 miles from the ZIP's center: its last spring frost comes after January 8 in half of years and after February 18 in one year in ten.
| Station | Distance | Elevation | Last frost (median) | 1 in 10 after | First frost (median) | Hardiness zone |
|---|---|---|---|---|---|---|
| Pomona, CAPomona/Fairplex | 7 mi | 999 ft | January 8 | February 18 | December 28 | – |
| San Gabriel, CASan Gabriel Fire Dept | 12 mi | 363 ft | January 4 | January 28 | January 2 | – |
| Mount Wilson CBS, CA | 16 mi | 5,710 ft | April 28 | May 27 | November 15 | 8b |
| Pasadena, CA | 16 mi | 864 ft | January 8 | February 17 | January 7 | 10b |
| Chino, CAChino Airport | 16 mi | 650 ft | January 17 | February 22 | December 19 | 9b |
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 Pomona
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) | March 9 | February 24 | February 8 | December 29 | December 10 | November 21 |
| 32°F | February 18 | January 26 | January 8 | December 14 | December 28 | December 5 |
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.