St. Ignatius, MT 59831 Frost Dates
59831, near St. Ignatius, MT: the frost window
Around 05/12 is the usual last spring frost, about 257 days away. Fall's first freeze usually shows up around 10/02, roughly 142 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts St. Ignatius in Zone 6a (-10 to -5°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
St. Ignatius'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.
The actual range around St. Ignatius's last frost
05/12 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/28 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 06/01 and only about 1 year in 10 sees frost after that.
St. Ignatius against the rest of the dataset
About 142 days separate St. Ignatius's last and first frost, putting it 36,775 of 40,283 ZIP codes nationally. Within MT, it ranks 58 of 392.
Learn more
Two guides worth reading on 59831: the frost range, on how to read the range around St. Ignatius's dates instead of trusting one, and local microclimates, on what one yard in St. Ignatius can differ from the 59831 normal.