Missoula, MT 59807 Frost Dates
59807, near Missoula, MT: the frost window
Typically, the last spring freeze lands around 05/10, roughly 255 days out. Fall's first freeze usually shows up around 10/01, roughly 143 days after the last spring frost.
Missoula sits in USDA Zone 6a (-10 to -5°F average annual minimum). The dates above are NOAA's 1991-2020 normal at the nearest reporting station, a 30-year average, not a forecast.
Stretching the season past the first frost
Missoula's growing season runs out in roughly 5 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
How much risk comes with planting early here
05/10 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/27 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/28 and only about 1 year in 10 sees frost after that.
Missoula against the rest of the dataset
About 143 days separate Missoula's last and first frost, putting it 36,490 of 40,283 ZIP codes nationally. Within MT, it ranks 42 of 392.
Learn more
Two guides worth reading on 59807: zone vs. frost date, on why Zone 6a and Missoula's frost date answer different questions, and the frost range, on how to read the range around Missoula's dates instead of trusting one.