Frost Dates for 83211 — American Falls, Idaho

Half of springs at American Falls, ID see their last 32°F night by May 4; only one in ten is past it by April 20, and one in ten still has one after May 21. Planting tender crops after May 10 leaves a 30% risk of a frost on them, after May 15 20%, and after May 21 10%. The 17 days between the even-odds date and the one-in-ten date is narrower than at 54% of the 67 Idaho stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 8 in half of years, as early as September 22 one year in ten, and holds off past October 24 one year in ten. A hard freeze of 28°F follows 13 days later, around October 21; in spring the one-in-ten date for 28°F is May 6, 15 days before the 32°F one. The freeze-free season lasts 155 days in a typical year, longer than at 64% of the 67 Idaho stations; it reaches 176 days one year in ten and falls short of 134 one year in ten. On average 145 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 16 days longer, to about May 20, and return around September 25. Severe cold of 16°F or below comes every winter, usually between November 20 and March 3.

July is the warmest month at American Falls, ID, averaging 90°F by day and 56°F at night; January is the coldest at 35°F and 19°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 62% of years.

Warmth for growing adds up to 2,554 growing degree days a year (base 50°F), more than at 66% of the 67 Idaho stations. 28% of them (725) have built up by the end of June, and July adds the most, 725. Precipitation totals 11.1 inches a year, most in May (1.5") and least in July (0.5"); May to September bring 41% of it.

The nearest other station, Aberdeen Exp Stn, ID, 15 miles north of American Falls, has a last frost 17 days later (May 21), a first frost 18 days earlier (September 20), a season 37 days shorter.

The first measurable snow (0.1 inch or more) in American Falls usually arrives around November 8, and the last of the season around April 17. Those are the middle dates across the winters of 1991–2020 at American Falls 6 NE, ID, 7.6 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 17 days after the last snow.

ZIP 83211 is 7 miles from American Falls, ID, which stands at 4,510 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 83211 in zone 6a, the band where the coldest night of the year averaged -10 to -5°F (-23.3 to -20.6°C) over 1991–2020; a zone describes winter lows, not frost dates.