Frost Dates for 99623 — Wasilla, Alaska

Half of springs at Anderson Lake, AK see their last 32°F night by May 16; only one in ten is past it by May 1, and one in ten still has one after May 31. Planting tender crops after May 23 leaves a 30% risk of a frost on them, after May 26 20%, and after May 31 10%. The 15 days between the even-odds date and the one-in-ten date is wider than at 70% of the 37 Alaska stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 23 in half of years, as early as September 8 one year in ten, and holds off past October 5 one year in ten. A hard freeze of 28°F follows 10 days later, around October 3; in spring the one-in-ten date for 28°F is May 16, 15 days before the 32°F one. The freeze-free season lasts 128 days in a typical year, shorter than at 54% of the 37 Alaska stations; it reaches 149 days one year in ten and falls short of 108 one year in ten. On average 194 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 16 days longer, to about June 1, and return around September 10. Severe cold of 16°F or below comes every winter, usually between October 29 and April 2.

July is the warmest month at Anderson Lake, AK, averaging 67°F by day and 50°F at night; January is the coldest at 24°F and 11°F. A freezing night is all but certain in every month from October 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 637 growing degree days a year (base 50°F), fewer than at 54% of the 37 Alaska stations. 29% of them (182) have built up by the end of June, and July adds the most, 256. Precipitation totals 18.9 inches a year, most in August (3.4") and least in April (0.4"); May to September bring 62% of it.

The nearest other station, Eklutna Wtp, AK, 14 miles southeast of Wasilla and 182 feet higher, has a last frost 2 days later (May 18), a first frost 3 days earlier (September 20), a season 4 days shorter.

The first measurable snow (0.1 inch or more) in Wasilla usually arrives around October 14, and the last of the season around April 6. Those are the middle dates across the winters of 1991–2020 at Anderson Lake, AK, 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 40 days after the last snow.

ZIP 99623 is 8 miles from Anderson Lake, AK, which stands at 458 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 99654 (Wasilla). The 2023 USDA Plant Hardiness Zone Map lists ZIP 99623 in zone 4b, the band where the coldest night of the year averaged -25 to -20°F (-31.7 to -28.9°C) over 1991–2020; a zone describes winter lows, not frost dates.