Frost Dates for 99901 — Ketchikan, Alaska

Half of springs at Beaver Falls, AK see their last 32°F night by April 4; only one in ten is past it by March 15, and one in ten still has one after April 25. Planting tender crops after April 13 leaves a 30% risk of a frost on them, after April 19 20%, and after April 25 10%. The 21 days between the even-odds date and the one-in-ten date is wider than at 95% of the 37 Alaska stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.

In fall the first 32°F night comes by November 9 in half of years, as early as October 19 one year in ten, and holds off past December 2 one year in ten. A hard freeze of 28°F follows 17 days later, around November 26; in spring the one-in-ten date for 28°F is April 5, 20 days before the 32°F one. The freeze-free season lasts 218 days in a typical year, the longest of the 37 Alaska stations; it reaches 248 days one year in ten and falls short of 191 one year in ten. On average 67 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 23 days longer, to about April 27, and return around October 22. Nights of 24°F, cold enough to damage hardier plants, come in 98% of winters and 16°F in 48%.

August is the warmest month at Beaver Falls, AK, averaging 67°F by day and 54°F at night; January is the coldest at 39°F and 32°F. A freezing night is all but certain in every month from December to March (a 90% chance or more). From May to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 56% of years.

Warmth for growing adds up to 1,165 growing degree days a year (base 50°F), the most of the 37 Alaska stations. 29% of them (333) have built up by the end of June, and August adds the most, 327. Precipitation totals 157.3 inches a year, most in November (19.5") and least in June (5.9"); May to September bring 31% of it.

The first measurable snow (0.1 inch or more) in Ketchikan usually arrives around November 17, and the last of the season around April 4. Those are the middle dates across the winters of 1991–2020 at Annette Island Airport, AK, 23.1 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 on the day of the last snow.

ZIP 99901 is 1 mile from Beaver Falls, AK, which stands at 35 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 99901 in zone 7b, the band where the coldest night of the year averaged 5 to 10°F (-15.0 to -12.2°C) over 1991–2020; a zone describes winter lows, not frost dates.