Frost Dates for 98057 — Renton, Washington

Half of springs at Cedar Lake, WA see their last 32°F night by April 23; only one in ten is past it by April 3, and one in ten still has one after May 13. Planting tender crops after May 2 leaves a 30% risk of a frost on them, after May 6 20%, and after May 13 10%. The 20 days between the even-odds date and the one-in-ten date is wider than at 52% of the 113 Washington stations behind this site's ZIP pages.

In fall the first 32°F night comes by November 1 in half of years, as early as October 17 one year in ten, and holds off past November 22 one year in ten. A hard freeze of 28°F follows 21 days later, around November 22; in spring the one-in-ten date for 28°F is April 21, 22 days before the 32°F one. The freeze-free season lasts 193 days in a typical year, longer than at 52% of the 113 Washington stations; it reaches 222 days one year in ten and falls short of 169 one year in ten. On average 86 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 17 days longer, to about May 10, and return around October 16. Nights of 24°F, cold enough to damage hardier plants, come in 98% of winters and 16°F in 43%.

August is the warmest month at Cedar Lake, WA, averaging 71°F by day and 52°F at night; December is the coldest at 39°F and 31°F. A freezing night is all but certain in every month from November to March (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 89% of years and May still brings one in 32% of years.

Warmth for growing adds up to 1,171 growing degree days a year (base 50°F), fewer than at 99% of the 113 Washington stations. 23% of them (271) have built up by the end of June, and August adds the most, 346. Precipitation totals 99.9 inches a year, most in November (14.6") and least in July (2.1"); May to September bring 22% of it.

The nearest other station, Snoqualmie Falls, WA, 8 miles north of Renton and 1,120 feet lower, has a last frost 24 days earlier (March 30), a first frost 6 days later (November 7), a season 30 days longer.

The first measurable snow (0.1 inch or more) in Renton usually arrives around November 29, and the last of the season around April 5. Those are the middle dates across the winters of 1991–2020 at Cedar Lake, WA, 2.5 miles away: half of years saw snow earlier, half later. Every one of those winters saw snow. The last 32°F night of spring typically comes 18 days after the last snow.

ZIP 98057 is 3 miles from Cedar Lake, WA, which stands at 1,560 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station; its figures are presented in full for 98045 (North Bend). The 2023 USDA Plant Hardiness Zone Map lists ZIP 98057 in zone 9a, the band where the coldest night of the year averaged 20 to 25°F (-6.7 to -3.9°C) over 1991–2020; a zone describes winter lows, not frost dates.