Frost Dates for 99011 — Fairchild Afb, Washington

Half of springs at Spokane WFO, WA see their last 32°F night by May 10; only one in ten is past it by April 25, and one in ten still has one after May 30. Planting tender crops after May 17 leaves a 30% risk of a frost on them, after May 22 20%, and after May 30 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 September 26 in half of years, as early as September 11 one year in ten, and holds off past October 8 one year in ten. A hard freeze of 28°F follows 11 days later, around October 7; in spring the one-in-ten date for 28°F is May 11, 19 days before the 32°F one. The freeze-free season lasts 137 days in a typical year, shorter than at 91% of the 113 Washington stations; it reaches 158 days one year in ten and falls short of 113 one year in ten. On average 157 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 31, and return around September 12. Severe cold of 16°F or below comes every winter, usually between November 16 and February 27.

July is the warmest month at Spokane WFO, WA, averaging 83°F by day and 52°F at night; December is the coldest at 32°F and 22°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 76% of years.

Warmth for growing adds up to 1,843 growing degree days a year (base 50°F), fewer than at 63% of the 113 Washington stations. 25% of them (468) have built up by the end of June, and July adds the most, 545. Precipitation totals 17.3 inches a year, most in December (2.4") and least in August (0.4"); May to September bring 26% of it.

The nearest other station, Spokane International Airport, WA, 7 miles east of Fairchild Afb, has a last frost 14 days earlier (April 26), a first frost 16 days later (October 12), a season 31 days longer.

The first measurable snow (0.1 inch or more) in Fairchild Afb usually arrives around November 10, and the last of the season around April 6. Those are the middle dates across the winters of 1991–2020 at Spokane WFO, WA, 6.3 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 34 days after the last snow.

ZIP 99011 is 6 miles from Spokane WFO, WA, which stands at 2,392 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 3 other ZIP codes share the station; its figures are presented in full for 99022 (Medical Lake). The 2023 USDA Plant Hardiness Zone Map lists ZIP 99011 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.