Frost Dates for 83530 — Grangeville, Idaho

Half of springs at Grangeville, ID see their last 32°F night by May 9; only one in ten is past it by April 24, and one in ten still has one after May 27. Planting tender crops after May 15 leaves a 30% risk of a frost on them, after May 20 20%, and after May 27 10%. The 18 days between the even-odds date and the one-in-ten date is narrower than at 42% of the 67 Idaho stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 3 in half of years, as early as September 14 one year in ten, and holds off past October 17 one year in ten. A hard freeze of 28°F follows 12 days later, around October 15; in spring the one-in-ten date for 28°F is May 8, 19 days before the 32°F one. The freeze-free season lasts 146 days in a typical year, shorter than at 55% of the 67 Idaho stations; it reaches 167 days one year in ten and falls short of 119 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 19 days longer, to about May 28, and return around September 19. Severe cold of 16°F or below comes every winter, usually between November 23 and February 28.

July is the warmest month at Grangeville, ID, averaging 82°F by day and 54°F at night; December is the coldest at 37°F and 24°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 74% of years.

Warmth for growing adds up to 1,888 growing degree days a year (base 50°F), fewer than at 73% of the 67 Idaho stations. 24% of them (445) have built up by the end of June, and July adds the most, 555. Precipitation totals 23.5 inches a year, most in May (3.4") and least in August (0.9"); May to September bring 43% of it.

The nearest other station, Cottonwood 2 WSW, ID, 15 miles northwest of Grangeville and 645 feet higher, has a last frost 3 days earlier (May 6), a first frost 10 days later (October 13), a season 10 days longer.

The first measurable snow (0.1 inch or more) in Grangeville usually arrives around November 15, and the last of the season around April 3. Those are the middle dates across the winters of 1991–2020 at Grangeville, ID, 1.4 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 83530 is 1 mile from Grangeville, ID, which stands at 3,300 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 83530 in zone 6b, the band where the coldest night of the year averaged -5 to 0°F (-20.6 to -17.8°C) over 1991–2020; a zone describes winter lows, not frost dates.