Frost Dates for 99709 — Fairbanks, Alaska

Half of springs at University Exp Stn, 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 30. Planting tender crops after May 21 leaves a 30% risk of a frost on them, after May 25 20%, and after May 30 10%. The 14 days between the even-odds date and the one-in-ten date is wider than at 57% of the 37 Alaska stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 8 in half of years, as early as August 26 one year in ten, and holds off past September 21 one year in ten. A hard freeze of 28°F follows 12 days later, around September 20; in spring the one-in-ten date for 28°F is May 20, 10 days before the 32°F one. The freeze-free season lasts 114 days in a typical year, shorter than at 73% of the 37 Alaska stations; it reaches 132 days one year in ten and falls short of 97 one year in ten. On average 228 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 13 days longer, to about May 29, and return around August 27. Severe cold of 16°F or below comes every winter, usually between October 13 and April 16.

July is the warmest month at University Exp Stn, AK, averaging 73°F by day and 51°F at night; January is the coldest at 3°F and -13°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 972 growing degree days a year (base 50°F), more than at 95% of the 37 Alaska stations. 39% of them (377) have built up by the end of June, and July adds the most, 367. Precipitation totals 13.0 inches a year, most in July (2.5") and least in April (0.3"); May to September bring 68% of it.

The nearest other station, Aurora, AK, 4 miles east of Fairbanks, has the same 50% last-frost date, a first frost 2 days earlier (September 6), a season 2 days shorter.

The first measurable snow (0.1 inch or more) in Fairbanks usually arrives around October 6, and the last of the season around April 10. Those are the middle dates across the winters of 1991–2020 at University Exp Stn, AK, 0.4 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 36 days after the last snow.

ZIP 99709 is under a mile from University Exp Stn, AK, which stands at 475 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 99709 in zone 3b, the band where the coldest night of the year averaged -35 to -30°F (-37.2 to -34.4°C) over 1991–2020; a zone describes winter lows, not frost dates.