Frost Dates for 83350 — Rupert, Idaho

Half of springs at Minidoka Dam, ID see their last 32°F night by May 16; only one in ten is past it by April 30, and one in ten still has one after June 5. Planting tender crops after May 24 leaves a 30% risk of a frost on them, after May 30 20%, and after June 5 10%. The 20 days between the even-odds date and the one-in-ten date is wider than at 69% of the 67 Idaho stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 1 in half of years, as early as September 13 one year in ten, and holds off past October 16 one year in ten. A hard freeze of 28°F follows 14 days later, around October 15; in spring the one-in-ten date for 28°F is May 19, 17 days before the 32°F one. The freeze-free season lasts 136 days in a typical year, shorter than at 63% of the 67 Idaho stations; it reaches 159 days one year in ten and falls short of 108 one year in ten. On average 166 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 18 days longer, to about June 3, and return around September 15. Severe cold of 16°F or below comes every winter, usually between November 10 and March 7.

July is the warmest month at Minidoka Dam, ID, averaging 89°F by day and 54°F at night; January is the coldest at 37°F and 18°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From July to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 87% of years and June still brings one in 18% of years.

Warmth for growing adds up to 2,425 growing degree days a year (base 50°F), more than at 60% of the 67 Idaho stations. 28% of them (670) have built up by the end of June, and July adds the most, 673. Precipitation totals 10.0 inches a year, most in May (1.3") and least in July (0.2"); May to September bring 32% of it.

The nearest other station, Paul 1ENE, ID, 8 miles southwest of Rupert, has a last frost 10 days earlier (May 6), a first frost 5 days later (October 6), a season 15 days longer.

The first measurable snow (0.1 inch or more) in Rupert usually arrives around November 20, and the last of the season around March 11. Those are the middle dates across the winters of 1991–2020 at Minidoka Dam, ID, 6.5 miles away: half of years saw snow earlier, half later. Snow fell in 93% of those winters. The last 32°F night of spring typically comes 66 days after the last snow.

ZIP 83350 is 7 miles from Minidoka Dam, ID, which stands at 4,164 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 83350 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.