Frost Dates for 98240 — Custer, Washington

Half of springs at Blaine, WA see their last 32°F night by March 31; only one in ten is past it by March 8, and one in ten still has one after April 22. Planting tender crops after April 7 leaves a 30% risk of a frost on them, after April 12 20%, and after April 22 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 November 4 in half of years, as early as October 18 one year in ten, and holds off past November 24 one year in ten. A hard freeze of 28°F follows 15 days later, around November 19; in spring the one-in-ten date for 28°F is March 31, 22 days before the 32°F one. The freeze-free season lasts 219 days in a typical year, longer than at 72% of the 113 Washington stations; it reaches 247 days one year in ten and falls short of 190 one year in ten. On average 52 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 23 days longer, to about April 23, and return around October 20. Nights of 24°F, cold enough to damage hardier plants, come in 97% of winters and 16°F in 36%.

July is the warmest month at Blaine, WA, averaging 73°F by day and 55°F at night; December is the coldest at 44°F and 34°F. A freezing night is all but certain in every month from November to March (a 90% chance or more). From May to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 44% of years.

Warmth for growing adds up to 1,754 growing degree days a year (base 50°F), fewer than at 72% of the 113 Washington stations. 31% of them (550) have built up by the end of June, and July adds the most, 432. Precipitation totals 41.8 inches a year, most in January (6.2") and least in July (1.1"); May to September bring 21% of it.

The nearest other station, Bellingham International Airport, WA, 10 miles southeast of Custer, has the same 50% last-frost date, a first frost 5 days earlier (October 30), a season 8 days shorter.

The first measurable snow (0.1 inch or more) in Custer usually arrives around December 19, and the last of the season around February 28. Those are the middle dates across the winters of 1991–2020 at Clearbrook, WA, 14 miles away: half of years saw snow earlier, half later. Snow fell in 95% of those winters. The last 32°F night of spring typically comes 31 days after the last snow.

ZIP 98240 is 8 miles from Blaine, WA, which stands at 60 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 98230 (Blaine). The 2023 USDA Plant Hardiness Zone Map lists ZIP 98240 in zone 8b, the band where the coldest night of the year averaged 15 to 20°F (-9.4 to -6.7°C) over 1991–2020; a zone describes winter lows, not frost dates.