Frost Dates for 99328 — Dayton, Washington

Half of springs at Dayton 1 WSW, WA see their last 32°F night by April 28; only one in ten is past it by April 11, and one in ten still has one after May 14. Planting tender crops after May 4 leaves a 30% risk of a frost on them, after May 8 20%, and after May 14 10%. The 16 days between the even-odds date and the one-in-ten date is narrower than at 74% of the 113 Washington stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 13 in half of years, as early as September 30 one year in ten, and holds off past October 29 one year in ten. A hard freeze of 28°F follows 12 days later, around October 25; in spring the one-in-ten date for 28°F is April 28, 16 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 190 days one year in ten and falls short of 147 one year in ten. On average 113 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 14 days longer, to about May 12, and return around October 1. Severe cold of 16°F or below comes in 97% of winters, usually between December 9 and February 5.

July is the warmest month at Dayton 1 WSW, WA, averaging 88°F by day and 55°F at night; December is the coldest at 41°F and 27°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 40% of years.

Warmth for growing adds up to 2,541 growing degree days a year (base 50°F), more than at 78% of the 113 Washington stations. 30% of them (753) have built up by the end of June, and July adds the most, 659. Precipitation totals 18.7 inches a year, most in November (2.4") and least in July (0.4"); May to September bring 25% of it.

The nearest other station, Pomeroy, WA, 21 miles northeast of Dayton and 377 feet higher, has a last frost 4 days later (May 2), a first frost 9 days earlier (October 4), a season 13 days shorter.

The first measurable snow (0.1 inch or more) in Dayton usually arrives around December 4, and the last of the season around March 2. Those are the middle dates across the winters of 1991–2020 at Dayton 1 WSW, WA, 1.6 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 57 days after the last snow.

ZIP 99328 is 2 miles from Dayton 1 WSW, WA, which stands at 1,557 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 99328 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.