Frost Dates for 98944 — Sunnyside, Washington

Half of springs at Sunnyside, WA see their last 32°F night by May 1; only one in ten is past it by April 16, and one in ten still has one after May 18. Planting tender crops after May 7 leaves a 30% risk of a frost on them, after May 11 20%, and after May 18 10%. The 17 days between the even-odds date and the one-in-ten date is narrower than at 66% of the 113 Washington stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 6 in half of years, as early as September 25 one year in ten, and holds off past October 22 one year in ten. A hard freeze of 28°F follows 13 days later, around October 19; in spring the one-in-ten date for 28°F is May 1, 17 days before the 32°F one. The freeze-free season lasts 157 days in a typical year, shorter than at 81% of the 113 Washington stations; it reaches 177 days one year in ten and falls short of 137 one year in ten. On average 124 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 16, and return around September 25. Severe cold of 16°F or below comes in 99% of winters, usually between November 26 and February 16.

July is the warmest month at Sunnyside, WA, averaging 88°F by day and 54°F at night; December is the coldest at 37°F and 22°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 49% of years.

Warmth for growing adds up to 2,448 growing degree days a year (base 50°F), more than at 73% of the 113 Washington stations. 32% of them (774) have built up by the end of June, and July adds the most, 660. Precipitation totals 7.8 inches a year, most in December (1.2") and least in July (0.1"); May to September bring 28% of it.

The nearest other station, Sunnyside #2, WA, 2 miles west of Sunnyside, has a last frost 1 day earlier (April 30), a first frost 2 days later (October 8), a season 3 days longer.

The first measurable snow (0.1 inch or more) in Sunnyside usually arrives around December 14, and the last of the season around January 21. Those are the middle dates across the winters of 1991–2020 at Sunnyside, WA, 1.6 miles away: half of years saw snow earlier, half later. Snow fell in 94% of those winters. The last 32°F night of spring typically comes 100 days after the last snow.

ZIP 98944 is 2 miles from Sunnyside, WA, which stands at 747 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 98944 in zone 7b, the band where the coldest night of the year averaged 5 to 10°F (-15.0 to -12.2°C) over 1991–2020; a zone describes winter lows, not frost dates.