Frost Dates for 99688 — Willow, Alaska

Half of springs at Willow West, AK see their last 32°F night by May 15; only one in ten is past it by May 3, and one in ten still has one after May 28. Planting tender crops after May 21 leaves a 30% risk of a frost on them, after May 24 20%, and after May 28 10%. The 13 days between the even-odds date and the one-in-ten date is narrower than at 46% of the 37 Alaska stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 18 in half of years, as early as September 4 one year in ten, and holds off past September 28 one year in ten. A hard freeze of 28°F follows 9 days later, around September 27; in spring the one-in-ten date for 28°F is May 17, 11 days before the 32°F one. The freeze-free season lasts 126 days in a typical year, shorter than at 57% of the 37 Alaska stations; it reaches 145 days one year in ten and falls short of 107 one year in ten. On average 219 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 28, and return around September 7. Severe cold of 16°F or below comes every winter, usually between October 20 and April 8.

July is the warmest month at Willow West, AK, averaging 68°F by day and 52°F at night; January is the coldest at 15°F and -4°F. A freezing night is all but certain in every month from September to May (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month.

Warmth for growing adds up to 808 growing degree days a year (base 50°F), more than at 70% of the 37 Alaska stations. 31% of them (249) have built up by the end of June, and July adds the most, 313.

The nearest other station, Whites Crossing, AK, 7 miles southeast of Willow, has a last frost 14 days later (May 29), a first frost 11 days earlier (September 7), a season 26 days shorter.

The first measurable snow (0.1 inch or more) in Willow usually arrives around October 19, and the last of the season around April 5. Those are the middle dates across the winters of 1991–2020 at Willow West, AK, 3.5 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 40 days after the last snow.

ZIP 99688 is 4 miles from Willow West, AK, which stands at 205 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 99688 in zone 3b, the band where the coldest night of the year averaged -35 to -30°F (-37.2 to -34.4°C) over 1991–2020; a zone describes winter lows, not frost dates.