Frost Dates for 83402 — Idaho Falls, Idaho

Half of springs at Idaho Falls Fanning Field, ID see their last 32°F night by May 23; only one in ten is past it by May 7, and one in ten still has one after June 13. Planting tender crops after June 2 leaves a 30% risk of a frost on them, after June 7 20%, and after June 13 10%. The 21 days between the even-odds date and the one-in-ten date is wider than at 78% of the 67 Idaho stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.

In fall the first 32°F night comes by September 20 in half of years, as early as September 1 one year in ten, and holds off past October 4 one year in ten. A hard freeze of 28°F follows 12 days later, around October 2; in spring the one-in-ten date for 28°F is May 23, 21 days before the 32°F one. The freeze-free season lasts 114 days in a typical year, shorter than at 85% of the 67 Idaho stations; it reaches 139 days one year in ten and falls short of 88 one year in ten. On average 182 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 22 days longer, to about June 14, and return around September 5. Severe cold of 16°F or below comes every winter, usually between November 4 and March 16.

July is the warmest month at Idaho Falls Fanning Field, ID, averaging 87°F by day and 49°F at night; January is the coldest at 29°F and 12°F. A freezing night is all but certain in every month from October to May (a 90% chance or more). From July to August the chance of a 32°F night stays under 10% each month. In spring, June still brings one in 32% of years.

Warmth for growing adds up to 1,843 growing degree days a year (base 50°F), fewer than at 75% of the 67 Idaho stations. 26% of them (483) have built up by the end of June, and July adds the most, 556. Precipitation totals 10.3 inches a year, most in May (1.6") and least in July (0.5"); May to September bring 47% of it.

The nearest other station, Idaho Falls - Kifi, ID, 3 miles east of Idaho Falls, has a last frost 14 days earlier (May 9), a first frost 11 days later (October 1), a season 28 days longer.

The first measurable snow (0.1 inch or more) in Idaho Falls usually arrives around November 6, and the last of the season around March 30. Those are the middle dates across the winters of 1991–2020 at Idaho Falls - Kifi, ID, 3.3 miles away: half of years saw snow earlier, half later. Snow fell in 92% of those winters. The last 32°F night of spring typically comes 54 days after the last snow.

ZIP 83402 is 1 mile from Idaho Falls Fanning Field, ID, which stands at 4,729 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 83402 in zone 5b, the band where the coldest night of the year averaged -15 to -10°F (-26.1 to -23.3°C) over 1991–2020; a zone describes winter lows, not frost dates.