Prosser, WA 99350 Frost Dates
Frost dates for Prosser, WA, ZIP 99350
Typically, the last spring freeze lands around 04/14, roughly 229 days out. The first fall frost typically arrives around 10/22, about 189 frost-free days later.
Prosser sits in USDA Zone 7b (5 to 10°F average annual minimum). The dates above are NOAA's 1991-2020 normal at the nearest reporting station, a 30-year average, not a forecast.
What to do before the first frost
Zone 7b around Prosser has about 8 weeks left before the first fall frost — that's the usual window to get a cold frame up if you want to keep harvesting past it.
The actual range around Prosser's last frost
04/14 is the middle of 30 years of NOAA records, not a promise. Plant by 03/24 and you're betting against frost in roughly 9 years out of 10. 05/07 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Prosser compares
About 189 days separate Prosser's last and first frost, putting it 21,522 of 40,283 ZIP codes nationally. Within WA, it ranks 404 of 700.
Learn more
the frost range explains how to read the range around Prosser's dates instead of trusting one, and local microclimates explains what one yard in Prosser can differ from the 99350 normal.