Frost Dates for 99506 — Jber, Alaska

Half of springs at Anchorage Merrill Field, AK see their last 32°F night by May 1; only one in ten is past it by April 19, and one in ten still has one after May 9. Planting tender crops after May 4 leaves a 30% risk of a frost on them, after May 6 20%, and after May 9 10%. The 8 days between the even-odds date and the one-in-ten date is narrower than at 97% of the 37 Alaska stations behind this site's ZIP pages, so the end of frost is fairly predictable.

In fall the first 32°F night comes by September 29 in half of years, as early as September 17 one year in ten, and holds off past October 12 one year in ten. A hard freeze of 28°F follows 9 days later, around October 8; in spring the one-in-ten date for 28°F is May 1, 8 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 167 days one year in ten and falls short of 135 one year in ten. On average 184 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 11 days longer, to about May 12, and return around September 20. Severe cold of 16°F or below comes every winter, usually between November 1 and April 1.

July is the warmest month at Anchorage Merrill Field, AK, averaging 68°F by day and 54°F at night; January is the coldest at 23°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 55% of years.

Warmth for growing adds up to 958 growing degree days a year (base 50°F), more than at 92% of the 37 Alaska stations. 30% of them (289) have built up by the end of June, and July adds the most, 346. Precipitation totals 14.2 inches a year, most in September (3.0") and least in April (0.3"); May to September bring 62% of it.

The nearest other station, Fort Richardson Wtp, AK, 4 miles east of Jber and 332 feet higher, has a last frost 8 days later (May 9), a first frost 3 days earlier (September 26), a season 12 days shorter.

The first measurable snow (0.1 inch or more) in Jber usually arrives around October 22, and the last of the season around March 30. Those are the middle dates across the winters of 1991–2020 at Fort Richardson Wtp, AK, 4.1 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 32 days after the last snow.

ZIP 99506 is 3 miles from Anchorage Merrill Field, AK, which stands at 138 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 3 other ZIP codes share the station; its figures are presented in full for 99508 (Anchorage). The 2023 USDA Plant Hardiness Zone Map lists ZIP 99506 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.