Missoula, MT 59801 Frost Dates
Missoula, MT: when does the frost end?
The last spring frost here typically falls around 05/10, about 255 days from today. Fall's first freeze usually shows up around 10/01, roughly 143 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Missoula in Zone 5b (-15 to -10°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
Stretching the season past the first frost
With roughly 5 weeks until Missoula's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
Why 05/10 isn't a guarantee
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 36,487 of 40,283 ZIP codes nationally. Within MT, it ranks 39 of 392.
Learn more
Before leaning on 59801's figures: the frost range explains how to read the range around Missoula's dates instead of trusting one, while local microclimates explains what one yard in Missoula can differ from the 59801 normal.