Mercer Island, WA 98040 Frost Dates
Mercer Island, WA: when does the frost end?
Typically, the last spring freeze lands around 03/13, roughly 197 days out. Fall's first freeze usually shows up around 11/17, roughly 247 days after the last spring frost.
Mercer Island sits in USDA Zone 9a (20 to 25°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.
Stretching the season past the first frost
With roughly 12 weeks until Mercer Island's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
The actual range around Mercer Island's last frost
03/13 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 02/20 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 04/01 and only about 1 year in 10 sees frost after that.
Mercer Island against the rest of the dataset
About 247 days separate Mercer Island's last and first frost, putting it 7,792 of 40,283 ZIP codes nationally. Within WA, it ranks 149 of 700.
Learn more
Before leaning on 98040's figures: local microclimates explains what one yard in Mercer Island can differ from the 98040 normal, while zone vs. frost date explains why Zone 9a and Mercer Island's frost date answer different questions.