Frost Dates for 99703 — Fort Wainwright, Alaska

Half of springs at Aurora, AK see their last 32°F night by May 16; only one in ten is past it by May 5, and one in ten still has one after May 29. Planting tender crops after May 21 leaves a 30% risk of a frost on them, after May 25 20%, and after May 29 10%. The 13 days between the even-odds date and the one-in-ten date is narrower than at 46% of the 37 Alaska stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 6 in half of years, as early as August 25 one year in ten, and holds off past September 20 one year in ten. A hard freeze of 28°F follows 12 days later, around September 18; in spring the one-in-ten date for 28°F is May 19, 10 days before the 32°F one. The freeze-free season lasts 112 days in a typical year, shorter than at 78% of the 37 Alaska stations; it reaches 130 days one year in ten and falls short of 92 one year in ten. On average 227 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 27, and return around August 27. Severe cold of 16°F or below comes every winter, usually between October 11 and April 16.

July is the warmest month at Aurora, AK, averaging 73°F by day and 52°F at night; January is the coldest at 0°F and -15°F. A freezing night is all but certain in every month from September to May (a 90% chance or more). From June to July the chance of a 32°F night stays under 10% each month.

Warmth for growing adds up to 1,010 growing degree days a year (base 50°F), more than at 97% of the 37 Alaska stations. 40% of them (405) have built up by the end of June, and July adds the most, 380. Precipitation totals 12.8 inches a year, most in July (2.6") and least in March (0.3"); May to September bring 72% of it.

The nearest other station, University Exp Stn, AK, 7 miles west of Fort Wainwright, has the same 50% last-frost date, a first frost 2 days later (September 8), a season 2 days longer.

The first measurable snow (0.1 inch or more) in Fort Wainwright usually arrives around October 6, and the last of the season around April 15. Those are the middle dates across the winters of 1991–2020 at Aurora, AK, 3.4 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 31 days after the last snow.

ZIP 99703 is 3 miles from Aurora, AK, which stands at 443 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station; its figures are presented in full for 99701 (Fairbanks). The 2023 USDA Plant Hardiness Zone Map lists ZIP 99703 in zone 2a, the band where the coldest night of the year averaged -50 to -45°F (-45.6 to -42.8°C) over 1991–2020; a zone describes winter lows, not frost dates.