Frost Dates for 83226 — Challis, Idaho

Half of springs at Challis Airport, ID see their last 32°F night by May 14; only one in ten is past it by May 2, and one in ten still has one after June 2. Planting tender crops after May 20 leaves a 30% risk of a frost on them, after May 26 20%, and after June 2 10%. The 19 days between the even-odds date and the one-in-ten date is wider than at 60% of the 67 Idaho stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 25 in half of years, as early as September 10 one year in ten, and holds off past October 7 one year in ten. A hard freeze of 28°F follows 12 days later, around October 7; in spring the one-in-ten date for 28°F is May 12, 21 days before the 32°F one. The freeze-free season lasts 131 days in a typical year, shorter than at 67% of the 67 Idaho stations; it reaches 151 days one year in ten and falls short of 109 one year in ten. On average 193 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 21 days longer, to about June 4, and return around September 14. Severe cold of 16°F or below comes every winter, usually between November 8 and March 13.

July is the warmest month at Challis Airport, ID, averaging 87°F by day and 52°F at night; December is the coldest at 29°F and 11°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 11% of years.

Warmth for growing adds up to 1,959 growing degree days a year (base 50°F), fewer than at 64% of the 67 Idaho stations. 26% of them (511) have built up by the end of June, and July adds the most, 598. Precipitation totals 7.0 inches a year, most in May (0.9") and least in January (0.4"); May to September bring 51% of it.

The first measurable snow (0.1 inch or more) in Challis usually arrives around November 14, and the last of the season around April 2. Those are the middle dates across the winters of 1991–2020 at May 2SSE, ID, 14.6 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 42 days after the last snow.

ZIP 83226 is 2 miles from Challis Airport, ID, which stands at 5,033 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 83226 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.