Rosalia, WA 99170 Frost Dates
99170, near Rosalia, WA: the frost window
The last spring frost here typically falls around 05/30, about 275 days from today. Fall's first freeze usually shows up around 09/04, roughly 94 days after the last spring frost.
Zone 6b (-5 to 0°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 Rosalia, not a forecast for this year.
Stretching the season past the first frost
Rosalia's growing season runs out in roughly 1 week — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
Why 05/30 isn't a guarantee
05/30 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/09 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 07/13 and only about 1 year in 10 sees frost after that.
Rosalia against the rest of the dataset
Rosalia's growing season runs about 94 days, ranking 39,847 of 40,283 US ZIP codes measured here, longest to shortest. Within WA, it ranks 690 of 700.
Learn more
Two guides worth reading on 99170: zone vs. frost date, on why Zone 6b and Rosalia's frost date answer different questions, and the frost range, on how to read the range around Rosalia's dates instead of trusting one.