Frost Dates for 99347 — Pomeroy, Washington

Half of springs at Pomeroy, WA see their last 32°F night by May 2; only one in ten is past it by April 15, and one in ten still has one after May 19. Planting tender crops after May 9 leaves a 30% risk of a frost on them, after May 14 20%, and after May 19 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 4 in half of years, as early as September 17 one year in ten, and holds off past October 24 one year in ten. A hard freeze of 28°F follows 15 days later, around October 19; in spring the one-in-ten date for 28°F is May 4, 15 days before the 32°F one. The freeze-free season lasts 155 days in a typical year, shorter than at 82% of the 113 Washington stations; it reaches 182 days one year in ten and falls short of 131 one year in ten. On average 125 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 17 days longer, to about May 19, and return around September 19. Severe cold of 16°F or below comes in 99% of winters, usually between December 1 and February 15.

July is the warmest month at Pomeroy, WA, averaging 85°F by day and 53°F at night; December is the coldest at 40°F and 26°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 54% of years.

Warmth for growing adds up to 2,195 growing degree days a year (base 50°F), more than at 58% of the 113 Washington stations. 28% of them (614) have built up by the end of June, and July adds the most, 589. Precipitation totals 17.7 inches a year, most in November (2.3") and least in July (0.5"); May to September bring 25% of it.

The nearest other station, Dayton 1 WSW, WA, 22 miles southwest of Pomeroy and 377 feet lower, has a last frost 4 days earlier (April 28), a first frost 9 days later (October 13), a season 13 days longer.

The first measurable snow (0.1 inch or more) in Pomeroy usually arrives around November 29, and the last of the season around February 27. Those are the middle dates across the winters of 1991–2020 at Pomeroy, WA, 1.5 miles away: half of years saw snow earlier, half later. Snow fell in 50% of those winters. The last 32°F night of spring typically comes 64 days after the last snow.

ZIP 99347 is 2 miles from Pomeroy, WA, which stands at 1,934 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 99347 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.