Frost Dates for 98233 — Burlington, Washington

Half of springs at Mt Vernon 3 WNW, WA see their last 32°F night by March 24; only one in ten is past it by March 3, and one in ten still has one after April 14. Planting tender crops after April 1 leaves a 30% risk of a frost on them, after April 7 20%, and after April 14 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 3 in half of years, as early as October 12 one year in ten, and holds off past November 25 one year in ten. A hard freeze of 28°F follows 22 days later, around November 25; in spring the one-in-ten date for 28°F is March 17, 28 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 256 days one year in ten and falls short of 196 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 25 days longer, to about April 18, and return around October 16. Nights of 24°F, cold enough to damage hardier plants, come in 92% of winters and 16°F in 25%.

August is the warmest month at Mt Vernon 3 WNW, WA, averaging 75°F by day and 53°F at night; December is the coldest at 46°F and 35°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 89% of years and April still brings one in 32% of years.

Warmth for growing adds up to 1,764 growing degree days a year (base 50°F), fewer than at 70% of the 113 Washington stations. 31% of them (543) have built up by the end of June, and August adds the most, 439.

The nearest other station, Sedro-Woolley, WA, 5 miles east of Burlington, has a last frost 3 days later (March 27), a first frost 3 days later (November 6).

Measurable snow is rare here: only 6 of 18 winters from 1991 to 2020 recorded 0.1 inch or more at Anacortes, WA, 12.9 miles away, so there is no typical first-snow date to plan around.

ZIP 98233 is 4 miles from Mt Vernon 3 WNW, WA, which stands at 14 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 98273 (Mount Vernon). The 2023 USDA Plant Hardiness Zone Map lists ZIP 98233 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.