St. Mary's, AK 99658 Frost Dates
99658, near St. Mary's, AK: the frost window
The last spring frost here typically falls around 05/21, about 266 days from today. Fall's first freeze usually shows up around 09/22, roughly 122 days after the last spring frost.
Zone 4a (-30 to -25°F average annual minimum) comes from the USDA Plant Hardiness Zone Map; the frost dates above are the 1991-2020 normal at the nearest reporting NOAA station for St. Mary's, not a forecast for this year.
Stretching the season past the first frost
St. Mary's's growing season runs out in roughly 4 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
Why 05/21 isn't a guarantee
05/21 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/08 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 06/02 and only about 1 year in 10 sees frost after that.
St. Mary's against the rest of the dataset
About 122 days separate St. Mary's's last and first frost, putting it 38,965 of 40,283 ZIP codes nationally. Within AK, it ranks 114 of 269.
Learn more
Two guides worth reading on 99658: the frost range, on how to read the range around St. Mary's's dates instead of trusting one, and local microclimates, on what one yard in St. Mary's can differ from the 99658 normal.