Frost Dates for 83871 — Troy, Idaho

Half of springs at Potlatch 3 NNE, ID see their last 32°F night by May 15; only one in ten is past it by April 30, and one in ten still has one after June 2. Planting tender crops after May 23 leaves a 30% risk of a frost on them, after May 28 20%, and after June 2 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 September 21 in half of years, as early as August 31 one year in ten, and holds off past October 7 one year in ten. A hard freeze of 28°F follows 14 days later, around October 5; in spring the one-in-ten date for 28°F is May 13, 20 days before the 32°F one. The freeze-free season lasts 126 days in a typical year, shorter than at 73% of the 67 Idaho stations; it reaches 149 days one year in ten and falls short of 97 one year in ten. On average 153 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 26 days longer, to about June 10, and return around September 3. Severe cold of 16°F or below comes every winter, usually between November 24 and February 23.

August is the warmest month at Potlatch 3 NNE, ID, averaging 84°F by day and 48°F at night; December is the coldest at 36°F and 25°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). July is the only month with under a 10% chance of a 32°F night. In spring, May still brings one in 85% of years and June still brings one in 13% of years.

Warmth for growing adds up to 1,676 growing degree days a year (base 50°F), fewer than at 87% of the 67 Idaho stations. 24% of them (401) have built up by the end of June, and August adds the most, 488. Precipitation totals 24.7 inches a year, most in November (2.9") and least in July (0.8"); May to September bring 27% of it.

The nearest other station, Pullman Moscow Regional Airport, WA, 17 miles west of Troy and 209 feet lower, has a last frost 16 days earlier (April 29), a first frost 11 days later (October 2), a season 33 days longer.

The first measurable snow (0.1 inch or more) in Troy usually arrives around November 13, and the last of the season around April 5. Those are the middle dates across the winters of 1991–2020 at Moscow U Of I, ID, 10 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 40 days after the last snow.

ZIP 83871 is 16 miles from Potlatch 3 NNE, ID, which stands at 2,760 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 83844 (Moscow). The 2023 USDA Plant Hardiness Zone Map lists ZIP 83871 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.