Frost Dates for 98840 — Okanogan, Washington

Half of springs at Omak Airport, WA see their last 32°F night by April 30; only one in ten is past it by April 14, and one in ten still has one after May 15. Planting tender crops after May 6 leaves a 30% risk of a frost on them, after May 10 20%, and after May 15 10%. The 15 days between the even-odds date and the one-in-ten date is narrower than at 81% of the 113 Washington stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 7 in half of years, as early as September 23 one year in ten, and holds off past October 22 one year in ten. A hard freeze of 28°F follows 12 days later, around October 19; in spring the one-in-ten date for 28°F is May 2, 13 days before the 32°F one. The freeze-free season lasts 160 days in a typical year, shorter than at 80% of the 113 Washington stations; it reaches 183 days one year in ten and falls short of 139 one year in ten. On average 145 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 13 days longer, to about May 13, and return around September 28. Severe cold of 16°F or below comes every winter, usually between November 25 and February 17.

July is the warmest month at Omak Airport, WA, averaging 89°F by day and 58°F at night; December is the coldest at 33°F and 23°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 47% of years.

Warmth for growing adds up to 2,743 growing degree days a year (base 50°F), more than at 83% of the 113 Washington stations. 30% of them (816) have built up by the end of June, and July adds the most, 736. Precipitation totals 11.6 inches a year, most in December (2.0") and least in August (0.3"); May to September bring 29% of it.

The nearest other station, Chief Joseph Dam, WA, 24 miles south of Okanogan and 462 feet lower, has a last frost 4 days earlier (April 26), a first frost 4 days later (October 11), a season 7 days longer.

The first measurable snow (0.1 inch or more) in Okanogan usually arrives around November 28, and the last of the season around February 22. Those are the middle dates across the winters of 1991–2020 at Chief Joseph Dam, WA, 24.2 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 67 days after the last snow.

ZIP 98840 is 9 miles from Omak Airport, WA, which stands at 1,296 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 98841 (Omak). The 2023 USDA Plant Hardiness Zone Map lists ZIP 98840 in zone 7a, the band where the coldest night of the year averaged 0 to 5°F (-17.8 to -15.0°C) over 1991–2020; a zone describes winter lows, not frost dates.