Frost Dates for 99833 — Petersburg, Alaska

Half of springs at Petersburg 1, AK see their last 32°F night by April 29; only one in ten is past it by April 15, and one in ten still has one after May 14. Planting tender crops after May 4 leaves a 30% risk of a frost on them, after May 8 20%, and after May 14 10%. The 15 days between the even-odds date and the one-in-ten date is wider than at 70% of the 37 Alaska stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 17 in half of years, as early as September 30 one year in ten, and holds off past November 1 one year in ten. A hard freeze of 28°F follows 15 days later, around November 1; in spring the one-in-ten date for 28°F is April 30, 14 days before the 32°F one. The freeze-free season lasts 169 days in a typical year, longer than at 89% of the 37 Alaska stations; it reaches 189 days one year in ten and falls short of 145 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 15 days longer, to about May 14, and return around October 1. Severe cold of 16°F or below comes in 98% of winters, usually between December 14 and February 25.

July is the warmest month at Petersburg 1, AK, averaging 62°F by day and 51°F at night; January is the coldest at 35°F and 27°F. A freezing night is all but certain in every month from November 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 44% of years.

Warmth for growing adds up to 610 growing degree days a year (base 50°F), fewer than at 57% of the 37 Alaska stations. 27% of them (167) have built up by the end of June, and July adds the most, 198. Precipitation totals 110.3 inches a year, most in September (14.4") and least in June (5.0"); May to September bring 35% of it.

The nearest other station, Wrangell Airport, AK, 31 miles southeast of Petersburg, has a last frost 18 days earlier (April 11), a first frost 15 days later (November 1), a season 33 days longer.

The first measurable snow (0.1 inch or more) in Petersburg usually arrives around November 11, and the last of the season around April 3. Those are the middle dates across the winters of 1991–2020 at Petersburg 1, AK, 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 26 days after the last snow.

ZIP 99833 is 2 miles from Petersburg 1, AK, which stands at 107 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 99833 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.