Frost Dates for 99206 — Spokane Valley, Washington

Half of springs at Spokane Felts Field, WA see their last 32°F night by April 26; only one in ten is past it by April 10, and one in ten still has one after May 10. Planting tender crops after May 1 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 15 in half of years, as early as September 30 one year in ten, and holds off past October 31 one year in ten. A hard freeze of 28°F follows 12 days later, around October 27; in spring the one-in-ten date for 28°F is April 26, 14 days before the 32°F one. The freeze-free season lasts 170 days in a typical year, shorter than at 68% of the 113 Washington stations; it reaches 193 days one year in ten and falls short of 149 one year in ten. On average 123 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 13 days longer, to about May 9, and return around October 1. Severe cold of 16°F or below comes in 99% of winters, usually between December 5 and February 13.

July is the warmest month at Spokane Felts Field, WA, averaging 87°F by day and 56°F at night; December is the coldest at 37°F and 26°F. A freezing night is all but certain in every month from November 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 33% of years.

Warmth for growing adds up to 2,402 growing degree days a year (base 50°F), more than at 70% of the 113 Washington stations. 28% of them (678) have built up by the end of June, and July adds the most, 668. Precipitation totals 17.4 inches a year, most in December (2.2") and least in August (0.5"); May to September bring 29% of it.

The nearest other station, Spokane International Airport, WA, 13 miles west of Spokane Valley and 400 feet higher, has the same 50% last-frost date, a first frost 3 days earlier (October 12), a season 2 days shorter.

The first measurable snow (0.1 inch or more) in Spokane Valley 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, 12.6 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 99206 is 4 miles from Spokane Felts Field, WA, which stands at 1,953 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 17 other ZIP codes share the station; its figures are presented in full for 99208 (Spokane). The 2023 USDA Plant Hardiness Zone Map lists ZIP 99206 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.