Frost Dates for 99224 — Spokane, Washington

Half of springs at Spokane International Airport, WA see their last 32°F night by April 26; only one in ten is past it by April 9, and one in ten still has one after May 10. Planting tender crops after May 2 leaves a 30% risk of a frost on them, after May 5 20%, and after May 10 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 88% of the 113 Washington stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 12 in half of years, as early as September 29 one year in ten, and holds off past October 28 one year in ten. A hard freeze of 28°F follows 11 days later, around October 23; in spring the one-in-ten date for 28°F is April 28, 12 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 192 days one year in ten and falls short of 147 one year in ten. On average 132 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 12 days longer, to about May 8, and return around October 1. Severe cold of 16°F or below comes every winter, usually between November 30 and February 19.

July is the warmest month at Spokane International Airport, WA, averaging 84°F by day and 58°F at night; December is the coldest at 34°F and 24°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 35% of years.

Warmth for growing adds up to 2,313 growing degree days a year (base 50°F), more than at 64% of the 113 Washington stations. 27% of them (628) have built up by the end of June, and July adds the most, 651. Precipitation totals 16.6 inches a year, most in December (2.3") and least in July (0.4"); May to September bring 26% of it.

The nearest other station, Spokane WFO, WA, 7 miles northwest of Spokane, has a last frost 14 days later (May 10), a first frost 16 days earlier (September 26), a season 31 days shorter.

The first measurable snow (0.1 inch or more) in Spokane usually arrives around November 13, and the last of the season around April 4. Those are the middle dates across the winters of 1991–2020 at Spokane International Airport, WA, 1.8 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 22 days after the last snow.

ZIP 99224 is 2 miles from Spokane International Airport, WA, which stands at 2,353 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 99224 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.