Frost Dates for 99645 — Palmer, Alaska

Half of springs at Palmer Municipal Airport, AK see their last 32°F night by May 6; only one in ten is past it by April 24, and one in ten still has one after May 18. Planting tender crops after May 11 leaves a 30% risk of a frost on them, after May 13 20%, and after May 18 10%. The 12 days between the even-odds date and the one-in-ten date is narrower than at 65% of the 37 Alaska stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 25 in half of years, as early as September 11 one year in ten, and holds off past October 8 one year in ten. A hard freeze of 28°F follows 8 days later, around October 3; in spring the one-in-ten date for 28°F is May 6, 12 days before the 32°F one. The freeze-free season lasts 140 days in a typical year, longer than at 59% of the 37 Alaska stations; it reaches 156 days one year in ten and falls short of 123 one year in ten. On average 187 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 14 days longer, to about May 20, and return around September 14. Severe cold of 16°F or below comes every winter, usually between October 27 and April 2.

July is the warmest month at Palmer Municipal Airport, AK, averaging 68°F by day and 51°F at night; January is the coldest at 22°F and 8°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 76% of years.

Warmth for growing adds up to 759 growing degree days a year (base 50°F), more than at 59% of the 37 Alaska stations. 31% of them (239) have built up by the end of June, and July adds the most, 284. Precipitation totals 12.8 inches a year, most in August (2.3") and least in April (0.3"); May to September bring 59% of it.

The nearest other station, Anderson Lake, AK, 10 miles west of Palmer and 228 feet higher, has a last frost 10 days later (May 16), a first frost 2 days earlier (September 23), a season 12 days shorter.

The first measurable snow (0.1 inch or more) in Palmer usually arrives around October 14, and the last of the season around April 17. Those are the middle dates across the winters of 1991–2020 at Lazy Mountain, 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 19 days after the last snow.

ZIP 99645 is 2 miles from Palmer Municipal Airport, AK, which stands at 230 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 99645 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.