Frost Dates for 59911 — Bigfork, Montana

Half of springs at Bigfork 13 S, MT see their last 32°F night by May 1; only one in ten is past it by April 16, and one in ten still has one after May 16. Planting tender crops after May 5 leaves a 30% risk of a frost on them, after May 9 20%, and after May 16 10%. The 15 days between the even-odds date and the one-in-ten date is narrower than at 53% of the 68 Montana stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 15 in half of years, as early as September 30 one year in ten, and holds off past October 30 one year in ten. A hard freeze of 28°F follows 15 days later, around October 30; in spring the one-in-ten date for 28°F is April 28, 18 days before the 32°F one. The freeze-free season lasts 165 days in a typical year, the longest of the 68 Montana stations; it reaches 186 days one year in ten and falls short of 144 one year in ten. On average 127 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 15 days longer, to about May 16, and return around October 3. Severe cold of 16°F or below comes every winter, usually between December 3 and March 1.

July is the warmest month at Bigfork 13 S, MT, averaging 80°F by day and 55°F at night; January is the coldest at 34°F and 25°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 51% of years.

Warmth for growing adds up to 1,807 growing degree days a year (base 50°F), fewer than at 57% of the 68 Montana stations. 24% of them (442) have built up by the end of June, and July adds the most, 544. Precipitation totals 21.3 inches a year, most in June (3.2") and least in February (1.0"); May to September bring 46% of it.

The nearest other station, Polson, MT, 22 miles southwest of Bigfork, has a last frost 9 days later (May 10), a first frost 10 days earlier (October 5), a season 18 days shorter.

The first measurable snow (0.1 inch or more) in Bigfork usually arrives around November 28, and the last of the season around March 3. Those are the middle dates across the winters of 1991–2020 at Bigfork 13 S, MT, 6.2 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 59 days after the last snow.

ZIP 59911 is 6 miles from Bigfork 13 S, MT, which stands at 2,979 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 59911 in zone 5b, the band where the coldest night of the year averaged -15 to -10°F (-26.1 to -23.3°C) over 1991–2020; a zone describes winter lows, not frost dates.