Frost Dates for 99518 — Anchorage, Alaska

Half of springs at Anchorage Lake Hood Airport, AK see their last 32°F night by May 1; only one in ten is past it by April 20, and one in ten still has one after May 8. Planting tender crops after May 4 leaves a 30% risk of a frost on them, after May 5 20%, and after May 8 10%. The 7 days between the even-odds date and the one-in-ten date is the narrowest of the 37 Alaska stations behind this site's ZIP pages, so the end of frost is fairly predictable.

In fall the first 32°F night comes by October 3 in half of years, as early as September 22 one year in ten, and holds off past October 16 one year in ten. A hard freeze of 28°F follows 11 days later, around October 14; in spring the one-in-ten date for 28°F is May 1, 7 days before the 32°F one. The freeze-free season lasts 156 days in a typical year, longer than at 76% of the 37 Alaska stations; it reaches 170 days one year in ten and falls short of 142 one year in ten. On average 178 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 8 days longer, to about May 9, and return around September 23. Severe cold of 16°F or below comes every winter, usually between November 6 and April 1.

July is the warmest month at Anchorage Lake Hood Airport, AK, averaging 68°F by day and 54°F at night; January is the coldest at 23°F and 10°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 51% of years.

Warmth for growing adds up to 943 growing degree days a year (base 50°F), more than at 89% of the 37 Alaska stations. 30% of them (282) have built up by the end of June, and July adds the most, 338. Precipitation totals 15.1 inches a year, most in September (3.1") and least in April (0.4"); May to September bring 61% of it.

The nearest other station, Anchorage Forecast Office, AK, 3 miles west of Anchorage, has a last frost 4 days later (May 5), a first frost 4 days earlier (September 29), a season 9 days shorter.

The first measurable snow (0.1 inch or more) in Anchorage usually arrives around October 21, and the last of the season around April 17. Those are the middle dates across the winters of 1991–2020 at Anchorage Forecast Office, AK, 3.4 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 14 days after the last snow.

ZIP 99518 is 3 miles from Anchorage Lake Hood Airport, AK, which stands at 90 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 99517 (Anchorage). The 2023 USDA Plant Hardiness Zone Map lists ZIP 99518 in zone 5a, the band where the coldest night of the year averaged -20 to -15°F (-28.9 to -26.1°C) over 1991–2020; a zone describes winter lows, not frost dates.