Frost Dates for 59804 — Missoula, Montana

Half of springs at Missoula International Airport, MT see their last 32°F night by May 16; only one in ten is past it by May 3, and one in ten still has one after June 1. Planting tender crops after May 22 leaves a 30% risk of a frost on them, after May 27 20%, and after June 1 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 September 26 in half of years, as early as September 12 one year in ten, and holds off past October 8 one year in ten. A hard freeze of 28°F follows 10 days later, around October 6; in spring the one-in-ten date for 28°F is May 14, 18 days before the 32°F one. The freeze-free season lasts 130 days in a typical year, longer than at 57% of the 68 Montana stations; it reaches 149 days one year in ten and falls short of 107 one year in ten. On average 173 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 22 days longer, to about June 7, and return around September 14. Severe cold of 16°F or below comes every winter, usually between November 11 and March 6.

July is the warmest month at Missoula International Airport, MT, averaging 85°F by day and 52°F at night; December is the coldest at 31°F and 18°F. A freezing night is all but certain in every month from October to May (a 90% chance or more). From July to August the chance of a 32°F night stays under 10% each month. In spring, June still brings one in 11% of years.

Warmth for growing adds up to 1,843 growing degree days a year (base 50°F), fewer than at 51% of the 68 Montana stations. 25% of them (460) have built up by the end of June, and July adds the most, 572. Precipitation totals 14.3 inches a year, most in June (2.1") and least in August (0.8"); May to September bring 46% of it.

The nearest other station, Missoula 6 NW WFO, MT, 5 miles north of Missoula, has a last frost 10 days earlier (May 6), a first frost 8 days later (October 4), a season 21 days longer.

The first measurable snow (0.1 inch or more) in Missoula usually arrives around November 4, and the last of the season around April 17. Those are the middle dates across the winters of 1991–2020 at Missoula International Airport, MT, 4.6 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 29 days after the last snow.

ZIP 59804 is 5 miles from Missoula International Airport, MT, which stands at 3,192 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 59804 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.