Frost Dates for 99169 — Ritzville, Washington

Half of springs at Ritzville 1 SSE, WA see their last 32°F night by May 7; only one in ten is past it by April 25, and one in ten still has one after May 27. Planting tender crops after May 13 leaves a 30% risk of a frost on them, after May 18 20%, and after May 27 10%. The 20 days between the even-odds date and the one-in-ten date is wider than at 52% of the 113 Washington stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 10 in half of years, as early as September 27 one year in ten, and holds off past October 25 one year in ten. A hard freeze of 28°F follows 11 days later, around October 21; in spring the one-in-ten date for 28°F is May 10, 17 days before the 32°F one. The freeze-free season lasts 153 days in a typical year, shorter than at 84% of the 113 Washington stations; it reaches 174 days one year in ten and falls short of 127 one year in ten. On average 148 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 21 days longer, to about May 28, and return around September 28. Severe cold of 16°F or below comes in 99% of winters, usually between November 29 and February 8.

July is the warmest month at Ritzville 1 SSE, WA, averaging 87°F by day and 53°F at night; December is the coldest at 35°F and 23°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 70% of years.

Warmth for growing adds up to 2,247 growing degree days a year (base 50°F), more than at 61% of the 113 Washington stations. 26% of them (587) have built up by the end of June, and July adds the most, 622. Precipitation totals 12.7 inches a year, most in December (1.8") and least in August (0.3"); May to September bring 25% of it.

The nearest other station, Connell 1 W, WA, 37 miles southwest of Ritzville and 844 feet lower, has a last frost 7 days earlier (April 30), a first frost 2 days later (October 12), a season 12 days longer.

The first measurable snow (0.1 inch or more) in Ritzville usually arrives around November 27, and the last of the season around March 2. Those are the middle dates across the winters of 1991–2020 at Ritzville 1 SSE, WA, 2.9 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 66 days after the last snow.

ZIP 99169 is 3 miles from Ritzville 1 SSE, WA, which stands at 1,864 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 99169 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.