Frost Dates for 98278 — Oak Harbor, Washington

Half of springs at Whidbey Island NAS, WA see their last 32°F night by March 13; only one in ten is past it by February 20, and one in ten still has one after April 1. Planting tender crops after March 21 leaves a 30% risk of a frost on them, after March 27 20%, and after April 1 10%. The 19 days between the even-odds date and the one-in-ten date is narrower than at 49% of the 113 Washington stations behind this site's ZIP pages.

In fall the first 32°F night comes by November 14 in half of years, as early as October 26 one year in ten, and holds off past December 5 one year in ten. A hard freeze of 28°F follows 17 days later, around December 1; in spring the one-in-ten date for 28°F is March 12, 20 days before the 32°F one. The freeze-free season lasts 244 days in a typical year, longer than at 88% of the 113 Washington stations; it reaches 277 days one year in ten and falls short of 217 one year in ten. On average 40 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 9, and return around October 28. Nights of 24°F, cold enough to damage hardier plants, come in 82% of winters and 16°F in 15%.

August is the warmest month at Whidbey Island NAS, WA, averaging 70°F by day and 54°F at night; December is the coldest at 49°F and 38°F. A freezing night is all but certain in every month from December to January (a 90% chance or more). From May to September the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 90% of years and March still brings one in 73% of years and April still brings one in 11% of years.

Warmth for growing adds up to 1,664 growing degree days a year (base 50°F), fewer than at 82% of the 113 Washington stations. 32% of them (528) have built up by the end of June, and August adds the most, 366. Precipitation totals 19.9 inches a year, most in November (3.1") and least in July (0.6"); May to September bring 27% of it.

The nearest other station, Coupeville 1 S, WA, 7 miles south of Oak Harbor, has a last frost 4 days later (March 17), a first frost 3 days earlier (November 11), a season 7 days shorter.

Measurable snow is rare here: only 5 of 19 winters from 1991 to 2020 recorded 0.1 inch or more at Coupeville 1 S, WA, 7.3 miles away, so there is no typical first-snow date to plan around.

ZIP 98278 is 3 miles from Whidbey Island NAS, WA, which stands at 47 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station; its figures are presented in full for 98277 (Oak Harbor). The 2023 USDA Plant Hardiness Zone Map lists ZIP 98278 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.