Frost Dates for 83703 — Boise, Idaho

Half of springs at Boise 7 N, ID see their last 32°F night by May 17; only one in ten is past it by April 27, and one in ten still has one after June 10. Planting tender crops after May 28 leaves a 30% risk of a frost on them, after June 3 20%, and after June 10 10%. The 24 days between the even-odds date and the one-in-ten date is wider than at 93% 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 October 12 in half of years, as early as September 27 one year in ten, and holds off past October 30 one year in ten. A hard freeze of 28°F follows 12 days later, around October 24; in spring the one-in-ten date for 28°F is May 19, 22 days before the 32°F one. The freeze-free season lasts 147 days in a typical year, shorter than at 52% of the 67 Idaho stations; it reaches 172 days one year in ten and falls short of 120 one year in ten. On average 125 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 20 days longer, to about June 6, and return around September 29. Severe cold of 16°F or below comes every winter, usually between November 28 and February 17.

July is the warmest month at Boise 7 N, ID, averaging 88°F by day and 58°F at night; December is the coldest at 37°F and 23°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 78% of years and June still brings one in 25% of years.

Warmth for growing adds up to 2,549 growing degree days a year (base 50°F), more than at 64% of the 67 Idaho stations. 25% of them (641) have built up by the end of June, and July adds the most, 704. Precipitation totals 18.1 inches a year, most in December (2.6") and least in August (0.2"); May to September bring 24% of it.

The nearest other station, Boise Air Terminal, ID, 7 miles south of Boise and 1,071 feet lower, has a last frost 23 days earlier (April 24), a first frost 9 days later (October 21), a season 32 days longer.

The first measurable snow (0.1 inch or more) in Boise usually arrives around November 6, and the last of the season around April 22. Those are the middle dates across the winters of 1991–2020 at Boise 7 N, ID, 5.6 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 25 days after the last snow.

ZIP 83703 is 6 miles from Boise 7 N, ID, which stands at 3,885 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station; its figures are presented in full for 83616 (Eagle). The 2023 USDA Plant Hardiness Zone Map lists ZIP 83703 in zone 7a, the band where the coldest night of the year averaged 0 to 5°F (-17.8 to -15.0°C) over 1991–2020; a zone describes winter lows, not frost dates.