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 94531
The USDA's 2023 Plant Hardiness Zone Map puts ZIP 94531 in zone 9b (the coldest night of a typical year: 25 to 30°F).
The nearest station, Antioch, CA, is 2 miles from the ZIP's center: its last spring frost comes after January 12 in half of years and after February 1 in one year in ten. By the USDA's method its plant hardiness zone is 9b.
| Station | Distance | Elevation | Last frost (median) | 1 in 10 after | First frost (median) | Hardiness zone |
|---|---|---|---|---|---|---|
| Antioch, CAAntioch Pumping Plant #3 | 2 mi | 60 ft | January 12 | February 1 | December 19 | 9b |
| Mount Diablo Junction, CA | 10 mi | 2,170 ft | March 8 | April 15 | December 22 | 9b |
| Concord, CAConcord Buchanan Field | 15 mi | 18 ft | January 9 | February 12 | December 14 | 9b |
| Tracy Pumping Plant, CA | 15 mi | 61 ft | January 19 | February 17 | December 10 | 9b |
| Concord Wastewater Treatment Plant, CA | 16 mi | 40 ft | January 7 | February 1 | December 19 | 10a |
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 Antioch
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 12 | February 23 | February 8 | January 11 | December 4 | November 18 |
| 32°F | February 1 | January 22 | January 12 | December 20 | December 19 | November 29 |
| 28°F (hard freeze) | January 22 | January 10 | January 2 | December 16 | December 29 | December 9 |
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.