Frost Dates for 83605 — Caldwell, Idaho

Half of springs at Nampa Sugar Factory, ID see their last 32°F night by April 29; only one in ten is past it by April 15, and one in ten still has one after May 18. Planting tender crops after May 5 leaves a 30% risk of a frost on them, after May 9 20%, and after May 18 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 October 13 in half of years, as early as September 29 one year in ten, and holds off past October 28 one year in ten. A hard freeze of 28°F follows 12 days later, around October 25; in spring the one-in-ten date for 28°F is May 1, 17 days before the 32°F one. The freeze-free season lasts 164 days in a typical year, longer than at 73% of the 67 Idaho stations; it reaches 186 days one year in ten and falls short of 142 one year in ten. On average 132 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 17 days longer, to about May 16, and return around September 30. Severe cold of 16°F or below comes in 99% of winters, usually between December 1 and February 11.

July is the warmest month at Nampa Sugar Factory, ID, averaging 93°F by day and 57°F at night; January is the coldest at 40°F and 23°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 42% of years.

Warmth for growing adds up to 2,956 growing degree days a year (base 50°F), more than at 85% of the 67 Idaho stations. 31% of them (904) have built up by the end of June, and July adds the most, 784. Precipitation totals 11.2 inches a year, most in January (1.4") and least in August (0.2"); May to September bring 27% of it.

The nearest other station, Deer Flat Dam, ID, 7 miles southwest of Caldwell, has a last frost 6 days earlier (April 23), a first frost 5 days later (October 18), a season 14 days longer.

The first measurable snow (0.1 inch or more) in Caldwell usually arrives around December 5, and the last of the season around February 20. Those are the middle dates across the winters of 1991–2020 at Nampa Sugar Factory, ID, 6.4 miles away: half of years saw snow earlier, half later. Snow fell in 90% of those winters. The last 32°F night of spring typically comes 68 days after the last snow.

ZIP 83605 is 6 miles from Nampa Sugar Factory, ID, which stands at 2,470 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 6 other ZIP codes share the station; its figures are presented in full for 83646 (Meridian). The 2023 USDA Plant Hardiness Zone Map lists ZIP 83605 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.