Frost Dates for 59864 — Ronan, Montana

Half of springs at Polson, MT see their last 32°F night by May 10; only one in ten is past it by April 27, and one in ten still has one after May 26. Planting tender crops after May 17 leaves a 30% risk of a frost on them, after May 21 20%, and after May 26 10%. The 16 days between the even-odds date and the one-in-ten date is narrower than at 40% of the 68 Montana stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 5 in half of years, as early as September 22 one year in ten, and holds off past October 19 one year in ten. A hard freeze of 28°F follows 11 days later, around October 16; in spring the one-in-ten date for 28°F is May 13, 13 days before the 32°F one. The freeze-free season lasts 147 days in a typical year, longer than at 88% of the 68 Montana stations; it reaches 168 days one year in ten and falls short of 125 one year in ten. On average 147 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 28, and return around September 26. Severe cold of 16°F or below comes every winter, usually between November 18 and March 3.

July is the warmest month at Polson, MT, averaging 83°F by day and 53°F at night; December is the coldest at 33°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 August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 79% of years.

Warmth for growing adds up to 1,881 growing degree days a year (base 50°F), more than at 53% of the 68 Montana stations. 25% of them (475) have built up by the end of June, and July adds the most, 559. Precipitation totals 14.9 inches a year, most in June (2.4") and least in February (0.8"); May to September bring 48% of it.

The nearest other station, Saint Ignatius, MT, 16 miles south of Ronan, has a last frost 2 days later (May 12), a first frost 3 days earlier (October 2), a season 5 days shorter.

The first measurable snow (0.1 inch or more) in Ronan usually arrives around November 16, and the last of the season around March 16. Those are the middle dates across the winters of 1991–2020 at Skq Dam, MT, 10.8 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 55 days after the last snow.

ZIP 59864 is 10 miles from Polson, MT, which stands at 3,010 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 59860 (Polson). The 2023 USDA Plant Hardiness Zone Map lists ZIP 59864 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.