Superior, MT 59872 Frost Dates
59872, near Superior, MT: the frost window
Around 05/17 is the usual last spring frost, about 262 days away. Fall's first freeze usually shows up around 09/23, roughly 125 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Superior 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
Superior's growing season runs out in roughly 4 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
Why 05/17 isn't a guarantee
05/17 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/01 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 06/08 and only about 1 year in 10 sees frost after that.
Superior against the rest of the dataset
About 125 days separate Superior's last and first frost, putting it 38,777 of 40,283 ZIP codes nationally. Within MT, it ranks 173 of 392.
Learn more
Two guides worth reading on 59872: the frost range, on how to read the range around Superior's dates instead of trusting one, and local microclimates, on what one yard in Superior can differ from the 59872 normal.