Frost Dates for 98284 — Sedro Woolley, Washington

Half of springs at Sedro-Woolley, WA see their last 32°F night by March 27; only one in ten is past it by March 8, and one in ten still has one after April 17. Planting tender crops after April 3 leaves a 30% risk of a frost on them, after April 7 20%, and after April 17 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 6 in half of years, as early as October 15 one year in ten, and holds off past November 28 one year in ten. A hard freeze of 28°F follows 18 days later, around November 24; in spring the one-in-ten date for 28°F is March 22, 26 days before the 32°F one. The freeze-free season lasts 224 days in a typical year, longer than at 77% of the 113 Washington stations; it reaches 253 days one year in ten and falls short of 195 one year in ten. On average 46 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 26 days longer, to about April 22, and return around October 17. Nights of 24°F, cold enough to damage hardier plants, come in 97% of winters and 16°F in 33%.

August is the warmest month at Sedro-Woolley, WA, averaging 75°F by day and 53°F at night; December is the coldest at 45°F and 34°F. A freezing night is all but certain in every month from December to March (a 90% chance or more). From May to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 35% of years.

Warmth for growing adds up to 1,803 growing degree days a year (base 50°F), fewer than at 66% of the 113 Washington stations. 31% of them (553) have built up by the end of June, and August adds the most, 436. Precipitation totals 48.7 inches a year, most in November (7.0") and least in July (1.3"); May to September bring 24% of it.

The nearest other station, Mt Vernon 3 WNW, WA, 11 miles southwest of Sedro Woolley, has a last frost 3 days earlier (March 24), a first frost 3 days earlier (November 3).

The first measurable snow (0.1 inch or more) in Sedro Woolley usually arrives around December 17, and the last of the season around February 22. Those are the middle dates across the winters of 1991–2020 at Sedro-Woolley, WA, 3.6 miles away: half of years saw snow earlier, half later. Snow fell in 60% of those winters. The last 32°F night of spring typically comes 33 days after the last snow.

ZIP 98284 is 4 miles from Sedro-Woolley, WA, which stands at 60 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 98284 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.