Frost Dates for 59873 — Thompson Falls, Montana

Half of springs at Thompson Falls Ph, MT see their last 32°F night by May 7; only one in ten is past it by April 25, and one in ten still has one after May 19. Planting tender crops after May 11 leaves a 30% risk of a frost on them, after May 14 20%, and after May 19 10%. The 12 days between the even-odds date and the one-in-ten date is the narrowest of the 68 Montana stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 4 in half of years, as early as September 21 one year in ten, and holds off past October 19 one year in ten. A hard freeze of 28°F follows 14 days later, around October 18; in spring the one-in-ten date for 28°F is May 6, 13 days before the 32°F one. The freeze-free season lasts 150 days in a typical year, longer than at 93% of the 68 Montana stations; it reaches 170 days one year in ten and falls short of 132 one year in ten. On average 148 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 22, and return around September 21. Severe cold of 16°F or below comes every winter, usually between November 27 and February 26.

July is the warmest month at Thompson Falls Ph, MT, averaging 86°F by day and 53°F at night; December is the coldest at 33°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 74% of years.

Warmth for growing adds up to 2,106 growing degree days a year (base 50°F), more than at 69% of the 68 Montana stations. 26% of them (557) have built up by the end of June, and July adds the most, 606. Precipitation totals 22.1 inches a year, most in November (2.6") and least in July (0.9"); May to September bring 32% of it.

The nearest other station, Trout Creek Rs, MT, 21 miles northwest of Thompson Falls, has a last frost 13 days later (May 20), a first frost 13 days earlier (September 21), a season 28 days shorter.

The first measurable snow (0.1 inch or more) in Thompson Falls usually arrives around October 23, and the last of the season around May 1. Those are the middle dates across the winters of 1991–2020 at Libby 32 SSE, MT, 17.1 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 6 days after the last snow.

ZIP 59873 is 10 miles from Thompson Falls Ph, MT, which stands at 2,380 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 59873 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.