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 99338
The USDA's 2023 Plant Hardiness Zone Map puts ZIP 99338 in zone 7b (the coldest night of a typical year: 5 to 10°F).
The nearest station, Kennewick, WA, is 9 miles from the ZIP's center: its last spring frost comes after March 28 in half of years and after April 10 in one year in ten. By the USDA's method its plant hardiness zone is 8a.
| Station | Distance | Elevation | Last frost (median) | 1 in 10 after | First frost (median) | Hardiness zone |
|---|---|---|---|---|---|---|
| Kennewick, WA | 9 mi | 390 ft | March 28 | April 10 | October 30 | 8a |
| Richland, WA | 10 mi | 373 ft | April 6 | April 24 | October 24 | 7b |
| Pasco, WAPasco Tri Cities Airport | 10 mi | 407 ft | April 27 | May 10 | October 11 | 7a |
| McNary Dam, WA | 16 mi | 361 ft | March 27 | April 14 | November 4 | – |
| Eltopia (8 mi WSW), WA | 17 mi | 700 ft | April 21 | May 6 | October 22 | 7b |
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 Kennewick
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) | April 30 | April 21 | April 14 | March 30 | October 21 | October 7 |
| 32°F | April 10 | April 2 | March 28 | March 9 | October 30 | October 18 |
| 28°F (hard freeze) | March 29 | March 16 | March 8 | February 20 | November 11 | October 27 |
| 24°F | March 12 | March 2 | February 23 | January 25 | November 25 | November 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.