Frost Dates for 99163 — Pullman, Washington

Half of springs at Pullman 2 NW, WA see their last 32°F night by May 6; only one in ten is past it by April 22, and one in ten still has one after May 25. Planting tender crops after May 13 leaves a 30% risk of a frost on them, after May 18 20%, and after May 25 10%. The 19 days between the even-odds date and the one-in-ten date is narrower than at 49% of the 113 Washington stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 29 in half of years, as early as September 9 one year in ten, and holds off past October 15 one year in ten. A hard freeze of 28°F follows 13 days later, around October 12; in spring the one-in-ten date for 28°F is May 7, 18 days before the 32°F one. The freeze-free season lasts 143 days in a typical year, shorter than at 88% of the 113 Washington stations; it reaches 168 days one year in ten and falls short of 116 one year in ten. On average 127 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 26 days longer, to about June 1, and return around September 11. Severe cold of 16°F or below comes every winter, usually between November 28 and February 17.

August is the warmest month at Pullman 2 NW, WA, averaging 85°F by day and 50°F at night; December is the coldest at 37°F and 25°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 67% of years.

Warmth for growing adds up to 1,983 growing degree days a year (base 50°F), more than at 50% of the 113 Washington stations. 25% of them (504) have built up by the end of June, and August adds the most, 551. Precipitation totals 20.5 inches a year, most in December (2.8") and least in July (0.4"); May to September bring 22% of it.

The nearest other station, Pullman Moscow Regional Airport, WA, 4 miles east of Pullman, has a last frost 7 days earlier (April 29), a first frost 3 days later (October 2), a season 16 days longer.

The first measurable snow (0.1 inch or more) in Pullman usually arrives around November 21, and the last of the season around March 8. Those are the middle dates across the winters of 1991–2020 at Pullman 2 NW, WA, 1.9 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 59 days after the last snow.

ZIP 99163 is 2 miles from Pullman 2 NW, WA, which stands at 2,515 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 99163 in zone 6b, the band where the coldest night of the year averaged -5 to 0°F (-20.6 to -17.8°C) over 1991–2020; a zone describes winter lows, not frost dates.