Great Falls, MT 59404 Frost Dates
Great Falls, MT: when does the frost end?
Typically, the last spring freeze lands around 05/19, roughly 264 days out. Fall's first freeze usually shows up around 09/24, roughly 126 days after the last spring frost.
Great Falls sits in USDA Zone 4b (-25 to -20°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
With roughly 4 weeks until Great Falls's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
The actual range around Great Falls's last frost
05/19 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/07 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 06/02 and only about 1 year in 10 sees frost after that.
Great Falls against the rest of the dataset
Great Falls's growing season runs about 126 days, ranking 38,678 of 40,283 US ZIP codes measured here, longest to shortest. Within MT, it ranks 158 of 392.
Learn more
Before leaning on 59404's figures: the frost range explains how to read the range around Great Falls's dates instead of trusting one, while local microclimates explains what one yard in Great Falls can differ from the 59404 normal.