Frost Dates for 98148 — Burien, Washington

Half of springs at Seattle Tacoma International Airport, WA see their last 32°F night by March 2; only one in ten is past it by February 5, and one in ten still has one after March 23. Planting tender crops after March 12 leaves a 30% risk of a frost on them, after March 16 20%, and after March 23 10%. The 21 days between the even-odds date and the one-in-ten date is wider than at 65% of the 113 Washington stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.

In fall the first 32°F night comes by November 23 in half of years, as early as November 6 one year in ten, and holds off past December 15 one year in ten. A hard freeze of 28°F follows 17 days later, around December 10; in spring the one-in-ten date for 28°F is February 28, 23 days before the 32°F one. The freeze-free season lasts 266 days in a typical year, longer than at 98% of the 113 Washington stations; it reaches 298 days one year in ten and falls short of 239 one year in ten. On average 25 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 29 days longer, to about March 31, and return around November 7. Nights of 24°F, cold enough to damage hardier plants, come in 64% of winters and 16°F in 4%.

August is the warmest month at Seattle Tacoma International Airport, WA, averaging 78°F by day and 57°F at night; December is the coldest at 47°F and 37°F. A freezing night is all but certain in December (a 90% chance or more). From April to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 85% of years and March still brings one in 53% of years.

Warmth for growing adds up to 2,324 growing degree days a year (base 50°F), more than at 65% of the 113 Washington stations. 31% of them (713) have built up by the end of June, and August adds the most, 539. Precipitation totals 39.5 inches a year, most in November (6.3") and least in July (0.6"); May to September bring 17% of it.

The nearest other station, Kent, WA, 4 miles southeast of Burien and 340 feet lower, has a last frost 18 days later (March 20), a first frost 13 days earlier (November 10), a season 33 days shorter.

The first measurable snow (0.1 inch or more) in Burien usually arrives around December 18, and the last of the season around February 23. Those are the middle dates across the winters of 1991–2020 at Seattle Tacoma International Airport, WA, 0.8 miles away: half of years saw snow earlier, half later. Snow fell in 83% of those winters. The last 32°F night of spring typically comes 7 days after the last snow.

ZIP 98148 is under a mile from Seattle Tacoma International Airport, WA, which stands at 370 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 4 other ZIP codes share the station; its figures are presented in full for 98198 (Des Moines). The 2023 USDA Plant Hardiness Zone Map lists ZIP 98148 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.