Frost Dates for 59935 — Troy, Montana

Half of springs at Troy, MT see their last 32°F night by May 14; only one in ten is past it by April 29, and one in ten still has one after May 31. Planting tender crops after May 21 leaves a 30% risk of a frost on them, after May 25 20%, and after May 31 10%. The 17 days between the even-odds date and the one-in-ten date is wider than at 62% of the 68 Montana 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 9 one year in ten, and holds off past October 9 one year in ten. A hard freeze of 28°F follows 11 days later, around October 6; in spring the one-in-ten date for 28°F is May 14, 17 days before the 32°F one. The freeze-free season lasts 132 days in a typical year, longer than at 60% of the 68 Montana stations; it reaches 155 days one year in ten and falls short of 108 one year in ten. On average 152 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 19 days longer, to about June 2, and return around September 7. Severe cold of 16°F or below comes every winter, usually between November 22 and March 4.

July is the warmest month at Troy, MT, averaging 87°F by day and 49°F at night; January is the coldest at 33°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 85% of years.

Warmth for growing adds up to 1,931 growing degree days a year (base 50°F), more than at 56% of the 68 Montana stations. 28% of them (549) have built up by the end of June, and July adds the most, 560. Precipitation totals 24.4 inches a year, most in November (3.5") and least in August (0.7"); May to September bring 29% of it.

The nearest other station, Bonners Ferry, ID, 21 miles west of Troy, has a last frost 14 days earlier (April 30), a first frost 9 days later (October 4), a season 22 days longer.

The first measurable snow (0.1 inch or more) in Troy usually arrives around November 21, and the last of the season around March 12. Those are the middle dates across the winters of 1991–2020 at Bonners Ferry, ID, 20.5 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 63 days after the last snow.

ZIP 59935 is 13 miles from Troy, MT, which stands at 1,929 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 59935 in zone 6a, the band where the coldest night of the year averaged -10 to -5°F (-23.3 to -20.6°C) over 1991–2020; a zone describes winter lows, not frost dates.