Frost Dates for 83716 — Boise, Idaho

Half of springs at Arrowrock Dam, ID see their last 32°F night by April 28; only one in ten is past it by April 11, and one in ten still has one after May 16. Planting tender crops after May 4 leaves a 30% risk of a frost on them, after May 9 20%, and after May 16 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 14 in half of years, as early as October 1 one year in ten, and holds off past October 29 one year in ten. A hard freeze of 28°F follows 13 days later, around October 27; in spring the one-in-ten date for 28°F is April 30, 16 days before the 32°F one. The freeze-free season lasts 169 days in a typical year, longer than at 82% of the 67 Idaho stations; it reaches 192 days one year in ten and falls short of 143 one year in ten. On average 134 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 May 16, and return around October 4. Severe cold of 16°F or below comes every winter, usually between December 4 and February 17.

July is the warmest month at Arrowrock Dam, ID, averaging 92°F by day and 59°F at night; January is the coldest at 37°F and 22°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 37% of years.

Warmth for growing adds up to 2,878 growing degree days a year (base 50°F), more than at 82% of the 67 Idaho stations. 27% of them (786) have built up by the end of June, and July adds the most, 784.

The nearest other station, Boise Air Terminal, ID, 11 miles west of Boise and 421 feet lower, has a last frost 4 days earlier (April 24), a first frost 7 days later (October 21), a season 10 days longer.

The first measurable snow (0.1 inch or more) in Boise usually arrives around November 24, and the last of the season around March 7. Those are the middle dates across the winters of 1991–2020 at Arrowrock Dam, ID, 5.2 miles away: half of years saw snow earlier, half later. Snow fell in 88% of those winters. The last 32°F night of spring typically comes 52 days after the last snow.

ZIP 83716 is 5 miles from Arrowrock Dam, ID, which stands at 3,235 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 83716 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.