Frost Dates for 59808 — Missoula, Montana

Half of springs at Missoula 6 NW WFO, MT see their last 32°F night by May 6; only one in ten is past it by April 24, 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 15 20%, and after May 19 10%. The 13 days between the even-odds date and the one-in-ten date is narrower than at 74% 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 23 one year in ten, and holds off past October 16 one year in ten. A hard freeze of 28°F follows 11 days later, around October 15; in spring the one-in-ten date for 28°F is May 7, 12 days before the 32°F one. The freeze-free season lasts 151 days in a typical year, longer than at 94% of the 68 Montana stations; it reaches 169 days one year in ten and falls short of 134 one year in ten. On average 161 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 17 days longer, to about May 23, and return around September 25. Severe cold of 16°F or below comes every winter, usually between November 17 and March 2.

July is the warmest month at Missoula 6 NW WFO, MT, averaging 86°F by day and 54°F at night; December is the coldest at 32°F and 19°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 71% of years.

Warmth for growing adds up to 2,042 growing degree days a year (base 50°F), more than at 63% of the 68 Montana stations. 26% of them (533) have built up by the end of June, and July adds the most, 615. Precipitation totals 14.4 inches a year, most in June (2.2") and least in July (0.8"); May to September bring 47% of it.

The nearest other station, Missoula International Airport, MT, under a mile west of Missoula, has a last frost 10 days later (May 16), a first frost 8 days earlier (September 26), a season 21 days shorter.

The first measurable snow (0.1 inch or more) in Missoula usually arrives around November 3, and the last of the season around April 18. Those are the middle dates across the winters of 1991–2020 at Missoula 6 NW WFO, MT, 0.7 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 18 days after the last snow.

ZIP 59808 is under a mile from Missoula 6 NW WFO, MT, which stands at 3,197 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 59808 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.