Kwethluk, AK 99621 Frost Dates
Frost dates for Kwethluk, AK, ZIP 99621
Around 05/21 is the usual last spring frost, about 266 days away. The first fall frost typically arrives around 09/22, about 122 frost-free days later.
The USDA Plant Hardiness Zone Map puts Kwethluk in Zone 4a (-30 to -25°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
What to do before the first frost
Zone 4a around Kwethluk has about 4 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.
Why 05/21 isn't a guarantee
05/21 is the middle of 30 years of NOAA records, not a promise. Plant by 05/08 and you're betting against frost in roughly 9 years out of 10. 06/02 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Kwethluk compares
At roughly 122 frost-free days, Kwethluk places 38,954 of 40,283 ZIP codes in this dataset. Within AK, it ranks 106 of 269.
Learn more
the frost range explains how to read the range around Kwethluk's dates instead of trusting one, and local microclimates explains what one yard in Kwethluk can differ from the 99621 normal.