Frost Dates for 98029 — Issaquah, Washington

Half of springs at Snoqualmie Falls, WA see their last 32°F night by March 30; only one in ten is past it by March 4, and one in ten still has one after April 21. Planting tender crops after April 8 leaves a 30% risk of a frost on them, after April 13 20%, and after April 21 10%. The 22 days between the even-odds date and the one-in-ten date is wider than at 71% 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 7 in half of years, as early as October 22 one year in ten, and holds off past December 1 one year in ten. A hard freeze of 28°F follows 22 days later, around November 29; in spring the one-in-ten date for 28°F is March 25, 27 days before the 32°F one. The freeze-free season lasts 223 days in a typical year, longer than at 74% of the 113 Washington stations; it reaches 252 days one year in ten and falls short of 195 one year in ten. On average 54 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 27 days longer, to about April 26, and return around October 22. Nights of 24°F, cold enough to damage hardier plants, come in 83% of winters and 16°F in 10%.

August is the warmest month at Snoqualmie Falls, WA, averaging 77°F by day and 54°F at night; December is the coldest at 46°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 September the chance of a 32°F night stays under 10% each month. In spring, March still brings one in 88% of years and April still brings one in 45% of years.

Warmth for growing adds up to 1,889 growing degree days a year (base 50°F), fewer than at 58% of the 113 Washington stations. 29% of them (552) have built up by the end of June, and August adds the most, 471. Precipitation totals 63.1 inches a year, most in November (9.5") and least in July (1.2"); May to September bring 20% of it.

The nearest other station, Renton Municipal Airport, WA, 11 miles southwest of Issaquah and 411 feet lower, has a last frost 17 days earlier (March 13), a first frost 9 days later (November 16), a season 25 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, 14.9 miles away, so there is no typical first-snow date to plan around.

ZIP 98029 is 9 miles from Snoqualmie Falls, WA, which stands at 440 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 4 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 98029 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.