Frost Dates for 99835 — Sitka, Alaska

Half of springs at Sitka 1 NE, AK see their last 32°F night by May 3; only one in ten is past it by April 16, and one in ten still has one after May 19. Planting tender crops after May 10 leaves a 30% risk of a frost on them, after May 14 20%, and after May 19 10%. The 16 days between the even-odds date and the one-in-ten date is wider than at 81% of the 37 Alaska stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 18 in half of years, as early as October 1 one year in ten, and holds off past November 7 one year in ten. A hard freeze of 28°F follows 23 days later, around November 10; in spring the one-in-ten date for 28°F is April 30, 19 days before the 32°F one. The freeze-free season lasts 166 days in a typical year, longer than at 86% of the 37 Alaska stations; it reaches 194 days one year in ten and falls short of 143 one year in ten. On average 115 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 20 days longer, to about May 23, and return around October 2. Nights of 24°F, cold enough to damage hardier plants, come in 100% of winters and 16°F in 88%.

August is the warmest month at Sitka 1 NE, AK, averaging 62°F by day and 50°F at night; January is the coldest at 37°F and 29°F. A freezing night is all but certain in every month from November to April (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 57% of years.

Warmth for growing adds up to 491 growing degree days a year (base 50°F), fewer than at 81% of the 37 Alaska stations. 17% of them (84) have built up by the end of June, and August adds the most, 177. Precipitation totals 102.0 inches a year, most in October (14.8") and least in June (3.6"); May to September bring 36% of it.

The first measurable snow (0.1 inch or more) in Sitka usually arrives around November 9, and the last of the season around April 3. Those are the middle dates across the winters of 1991–2020 at Hidden Falls Hatchery, AK, 19.8 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 30 days after the last snow.

ZIP 99835 is under a mile from Sitka 1 NE, AK, which stands at 78 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 99835 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.