Frost Dates for 99507 — Anchorage, Alaska

Half of springs at Campbell Creek Sci Ctr, AK see their last 32°F night by May 28; only one in ten is past it by May 17, and one in ten still has one after June 6. Planting tender crops after June 1 leaves a 30% risk of a frost on them, after June 3 20%, and after June 6 10%. The 9 days between the even-odds date and the one-in-ten date is narrower than at 92% 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 September 12 in half of years, as early as August 30 one year in ten, and holds off past September 25 one year in ten. A hard freeze of 28°F follows 12 days later, around September 24; in spring the one-in-ten date for 28°F is May 28, 9 days before the 32°F one. The freeze-free season lasts 107 days in a typical year, shorter than at 86% of the 37 Alaska stations; it reaches 124 days one year in ten and falls short of 89 one year in ten. On average 230 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 11 days longer, to about June 8, and return around September 1. Severe cold of 16°F or below comes every winter, usually between October 21 and April 7.

July is the warmest month at Campbell Creek Sci Ctr, AK, averaging 69°F by day and 49°F at night; January is the coldest at 19°F and 3°F. A freezing night is all but certain in every month from September to May (a 90% chance or more). July is the only month with under a 10% chance of a 32°F night. In spring, June still brings one in 32% of years.

Warmth for growing adds up to 606 growing degree days a year (base 50°F), fewer than at 59% of the 37 Alaska stations. 28% of them (168) have built up by the end of June, and July adds the most, 265.

The nearest other station, Anchorage Merrill Field, AK, 4 miles north of Anchorage, has a last frost 27 days earlier (May 1), a first frost 17 days later (September 29), a season 43 days longer.

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, 5.2 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 41 days after the last snow.

ZIP 99507 is 2 miles from Campbell Creek Sci Ctr, AK, which stands at 258 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 99504 (Anchorage). The 2023 USDA Plant Hardiness Zone Map lists ZIP 99507 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.