Frost Dates for 98010 — Black Diamond, Washington

Half of springs at Landsburg, WA see their last 32°F night by April 20; only one in ten is past it by March 31, and one in ten still has one after May 10. Planting tender crops after April 29 leaves a 30% risk of a frost on them, after May 4 20%, and after May 10 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 October 25 in half of years, as early as October 5 one year in ten, and holds off past November 12 one year in ten. A hard freeze of 28°F follows 18 days later, around November 12; in spring the one-in-ten date for 28°F is April 16, 24 days before the 32°F one. The freeze-free season lasts 187 days in a typical year, shorter than at 53% of the 113 Washington stations; it reaches 215 days one year in ten and falls short of 160 one year in ten. On average 70 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 20 days longer, to about May 10, and return around October 6. Nights of 24°F, cold enough to damage hardier plants, come in 98% of winters and 16°F in 34%.

August is the warmest month at Landsburg, WA, averaging 77°F by day and 52°F at night; December is the coldest at 45°F and 32°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 84% of years and May still brings one in 28% of years.

Warmth for growing adds up to 1,736 growing degree days a year (base 50°F), fewer than at 73% of the 113 Washington stations. 29% of them (506) have built up by the end of June, and August adds the most, 446. Precipitation totals 59.8 inches a year, most in November (8.5") and least in July (1.3"); May to September bring 21% of it.

The nearest other station, Buckley 1 NE, WA, 10 miles south of Black Diamond and 150 feet higher, has a last frost 13 days earlier (April 7), a first frost 5 days later (October 30), a season 17 days longer.

The first measurable snow (0.1 inch or more) in Black Diamond usually arrives around December 11, and the last of the season around February 27. Those are the middle dates across the winters of 1991–2020 at Palmer 3 ESE, WA, 7.7 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 52 days after the last snow.

ZIP 98010 is 5 miles from Landsburg, WA, which stands at 535 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 98038 (Maple Valley). The 2023 USDA Plant Hardiness Zone Map lists ZIP 98010 in zone 8b, the band where the coldest night of the year averaged 15 to 20°F (-9.4 to -6.7°C) over 1991–2020; a zone describes winter lows, not frost dates.