Frost Dates for 98168 — Tukwila, Washington

Half of springs at Seattle Boeing Field, WA see their last 32°F night by March 13; only one in ten is past it by February 20, and one in ten still has one after April 1. Planting tender crops after March 21 leaves a 30% risk of a frost on them, after March 25 20%, and after April 1 10%. The 19 days between the even-odds date and the one-in-ten date is narrower than at 49% of the 113 Washington stations behind this site's ZIP pages.

In fall the first 32°F night comes by November 17 in half of years, as early as November 1 one year in ten, and holds off past December 6 one year in ten. A hard freeze of 28°F follows 15 days later, around December 2; in spring the one-in-ten date for 28°F is March 10, 22 days before the 32°F one. The freeze-free season lasts 247 days in a typical year, longer than at 89% of the 113 Washington stations; it reaches 278 days one year in ten and falls short of 222 one year in ten. On average 30 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 21 days longer, to about April 3, and return around October 31. Nights of 24°F, cold enough to damage hardier plants, come in 81% of winters and 16°F in 9%.

August is the warmest month at Seattle Boeing Field, WA, averaging 77°F by day and 58°F at night; December is the coldest at 48°F and 36°F. A freezing night is all but certain in every month from December to February (a 90% chance or more). From May to October the chance of a 32°F night stays under 10% each month. In spring, March still brings one in 76% of years and April still brings one in 10% of years.

Warmth for growing adds up to 2,392 growing degree days a year (base 50°F), more than at 69% of the 113 Washington stations. 31% of them (751) have built up by the end of June, and August adds the most, 550. Precipitation totals 36.5 inches a year, most in November (5.8") and least in July (0.6"); May to September bring 16% of it.

The nearest other station, Seattle Tacoma International Airport, WA, 3 miles south of Tukwila and 350 feet higher, has a last frost 11 days earlier (March 2), a first frost 6 days later (November 23), a season 19 days longer.

Measurable snow is rare here: only 6 of 20 winters from 1991 to 2020 recorded 0.1 inch or more at Kent, WA, 5.8 miles away, so there is no typical first-snow date to plan around.

ZIP 98168 is 3 miles from Seattle Boeing Field, WA, which stands at 20 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 13 other ZIP codes share the station; its figures are presented in full for 98118 (Seattle). The 2023 USDA Plant Hardiness Zone Map lists ZIP 98168 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.