Frost Dates for 99181 — Valley, Washington

Half of springs at Chewelah, WA see their last 32°F night by May 16; only one in ten is past it by April 30, and one in ten still has one after June 7. Planting tender crops after May 25 leaves a 30% risk of a frost on them, after May 31 20%, and after June 7 10%. The 22 days between the even-odds date and the one-in-ten date is wider than at 71% of the 113 Washington stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.

In fall the first 32°F night comes by September 15 in half of years, as early as September 1 one year in ten, and holds off past September 29 one year in ten. A hard freeze of 28°F follows 13 days later, around September 28; in spring the one-in-ten date for 28°F is May 14, 24 days before the 32°F one. The freeze-free season lasts 120 days in a typical year, shorter than at 96% of the 113 Washington stations; it reaches 143 days one year in ten and falls short of 90 one year in ten. On average 170 nights a year drop to 32°F or below. Severe cold of 16°F or below comes every winter, usually between November 9 and March 3.

July is the warmest month at Chewelah, WA, averaging 86°F by day and 49°F at night; January is the coldest at 33°F and 20°F. A freezing night is all but certain in every month from September to April (a 90% chance or more). From July to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 88% of years and June still brings one in 16% of years.

Warmth for growing adds up to 1,864 growing degree days a year (base 50°F), fewer than at 60% of the 113 Washington stations. 29% of them (542) have built up by the end of June, and July adds the most, 541.

The nearest other station, Deer Park Airport, WA, 19 miles southeast of Valley and 521 feet higher, has a last frost 6 days later (May 22), a first frost 1 day earlier (September 14), a season 8 days shorter.

The first measurable snow (0.1 inch or more) in Valley usually arrives around November 25, and the last of the season around March 6. Those are the middle dates across the winters of 1991–2020 at Chewelah, WA, 8.9 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 71 days after the last snow.

ZIP 99181 is 9 miles from Chewelah, WA, which stands at 1,670 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 99109 (Chewelah). The 2023 USDA Plant Hardiness Zone Map lists ZIP 99181 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.