Frost Dates for 99737 — Delta Junction, Alaska

Half of springs at Big Delta Airport, AK see their last 32°F night by May 17; only one in ten is past it by May 3, and one in ten still has one after May 31. Planting tender crops after May 24 leaves a 30% risk of a frost on them, after May 28 20%, and after May 31 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 7 in half of years, as early as August 23 one year in ten, and holds off past September 22 one year in ten. A hard freeze of 28°F follows 13 days later, around September 20; in spring the one-in-ten date for 28°F is May 24, 7 days before the 32°F one. The freeze-free season lasts 113 days in a typical year, shorter than at 76% of the 37 Alaska stations; it reaches 134 days one year in ten and falls short of 93 one year in ten. On average 219 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 12 days longer, to about May 29, and return around August 27. Severe cold of 16°F or below comes every winter, usually between October 8 and April 14.

July is the warmest month at Big Delta Airport, AK, averaging 70°F by day and 52°F at night; January is the coldest at 6°F and -8°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 882 growing degree days a year (base 50°F), more than at 86% of the 37 Alaska stations. 37% of them (326) have built up by the end of June, and July adds the most, 334. Precipitation totals 10.3 inches a year, most in July (2.4") and least in January (0.2"); May to September bring 81% of it.

The first measurable snow (0.1 inch or more) in Delta Junction usually arrives around September 28, and the last of the season around April 17. Those are the middle dates across the winters of 1991–2020 at Delta 5 NE, AK, 8.6 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 30 days after the last snow.

ZIP 99737 is 8 miles from Big Delta Airport, AK, which stands at 1,277 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 99737 in zone 3a, the band where the coldest night of the year averaged -40 to -35°F (-40.0 to -37.2°C) over 1991–2020; a zone describes winter lows, not frost dates.