Frost Dates for 99801 — Juneau, Alaska

Half of springs at Juneau International Airport, AK see their last 32°F night by May 4; only one in ten is past it by April 23, and one in ten still has one after May 18. Planting tender crops after May 9 leaves a 30% risk of a frost on them, after May 13 20%, and after May 18 10%. The 14 days between the even-odds date and the one-in-ten date is wider than at 57% of the 37 Alaska stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 3 in half of years, as early as September 18 one year in ten, and holds off past October 20 one year in ten. A hard freeze of 28°F follows 15 days later, around October 18; in spring the one-in-ten date for 28°F is May 2, 16 days before the 32°F one. The freeze-free season lasts 150 days in a typical year, longer than at 68% of the 37 Alaska stations; it reaches 171 days one year in ten and falls short of 129 one year in ten. On average 128 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 17 days longer, to about May 21, and return around September 20. Severe cold of 16°F or below comes every winter, usually between November 29 and March 11.

July is the warmest month at Juneau International Airport, AK, averaging 64°F by day and 50°F at night; January is the coldest at 33°F and 24°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 66% of years.

Warmth for growing adds up to 646 growing degree days a year (base 50°F), fewer than at 51% of the 37 Alaska stations. 30% of them (193) have built up by the end of June, and July adds the most, 219. Precipitation totals 66.9 inches a year, most in September (9.2") and least in April (3.5"); May to September bring 42% of it.

The nearest other station, Juneau Dwtn, AK, 6 miles southeast of Juneau, has a last frost 14 days earlier (April 20), a first frost 19 days later (October 22), a season 33 days longer.

The first measurable snow (0.1 inch or more) in Juneau usually arrives around November 5, and the last of the season around March 31. Those are the middle dates across the winters of 1991–2020 at Juneau International Airport, AK, 0.6 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 34 days after the last snow.

ZIP 99801 is under a mile from Juneau International Airport, AK, which stands at 16 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 99801 in zone 6a, the band where the coldest night of the year averaged -10 to -5°F (-23.3 to -20.6°C) over 1991–2020; a zone describes winter lows, not frost dates.