Frost Dates for 98844 — Oroville, Washington

Half of springs at Tonasket 4 NNE, WA see their last 32°F night by April 26; only one in ten is past it by April 6, and one in ten still has one after May 11. Planting tender crops after May 2 leaves a 30% risk of a frost on them, after May 5 20%, and after May 11 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 10 in half of years, as early as September 28 one year in ten, and holds off past October 25 one year in ten. A hard freeze of 28°F follows 13 days later, around October 23; in spring the one-in-ten date for 28°F is April 20, 21 days before the 32°F one. The freeze-free season lasts 168 days in a typical year, shorter than at 71% of the 113 Washington stations; it reaches 193 days one year in ten and falls short of 147 one year in ten. On average 134 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 15 days longer, to about May 11, and return around September 29. Severe cold of 16°F or below comes every winter, usually between November 27 and February 16.

July is the warmest month at Tonasket 4 NNE, WA, averaging 88°F by day and 55°F at night; January is the coldest at 34°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 35% of years.

Warmth for growing adds up to 2,520 growing degree days a year (base 50°F), more than at 76% of the 113 Washington stations. 32% of them (806) have built up by the end of June, and July adds the most, 671.

The nearest other station, Omak Airport, WA, 33 miles south of Oroville and 336 feet higher, has a last frost 4 days later (April 30), a first frost 3 days earlier (October 7), a season 8 days shorter.

The first measurable snow (0.1 inch or more) in Oroville usually arrives around November 8, and the last of the season around March 14. Those are the middle dates across the winters of 1991–2020 at Republic, WA, 35.4 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 43 days after the last snow.

ZIP 98844 is 11 miles from Tonasket 4 NNE, WA, which stands at 960 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 98855 (Tonasket). The 2023 USDA Plant Hardiness Zone Map lists ZIP 98844 in zone 6a, the band where the coldest night of the year averaged -10 to -5°F (-23.3 to -20.6°C) over 1991–2020; a zone describes winter lows, not frost dates.