Seattle, WA 98103 Frost Dates
98103, near Seattle, WA: the frost window
Typically, the last spring freeze lands around 03/08, roughly 192 days out. Fall's first freeze usually shows up around 11/23, roughly 259 days after the last spring frost.
Zone 9a (20 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 Seattle, not a forecast for this year.
Stretching the season past the first frost
Seattle's growing season runs out in roughly 12 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
How much risk comes with planting early here
03/08 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 02/13 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 03/29 and only about 1 year in 10 sees frost after that.
Seattle against the rest of the dataset
About 259 days separate Seattle's last and first frost, putting it 6,507 of 40,283 ZIP codes nationally. Within WA, it ranks 23 of 700.
Learn more
Two guides worth reading on 98103: local microclimates, on what one yard in Seattle can differ from the 98103 normal, and zone vs. frost date, on why Zone 9a and Seattle's frost date answer different questions.