Thorne Bay, AK 99903 Frost Dates
99903, near Thorne Bay, AK: the frost window
Around 05/01 is the usual last spring frost, about 246 days away. Fall's first freeze usually shows up around 10/13, roughly 166 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Thorne Bay in Zone 7b (5 to 10°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
Stretching the season past the first frost
Thorne Bay's growing season runs out in roughly 7 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
Why 05/01 isn't a guarantee
05/01 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/17 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/16 and only about 1 year in 10 sees frost after that.
Thorne Bay against the rest of the dataset
At roughly 166 frost-free days, Thorne Bay places 30,433 of 40,283 ZIP codes in this dataset. Within AK, it ranks 22 of 269.
Learn more
Two guides worth reading on 99903: local microclimates, on what one yard in Thorne Bay can differ from the 99903 normal, and zone vs. frost date, on why Zone 7b and Thorne Bay's frost date answer different questions.