Colstrip, MT 59004 Frost Dates
59004, near Colstrip, MT: the frost window
Around 05/26 is the usual last spring frost, about 271 days away. Fall's first freeze usually shows up around 09/16, roughly 111 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Colstrip in Zone 4b (-25 to -20°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
Colstrip's growing season runs out in roughly 3 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 Colstrip's last frost
05/26 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/12 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 06/13 and only about 1 year in 10 sees frost after that.
Colstrip against the rest of the dataset
At roughly 111 frost-free days, Colstrip places 39,459 of 40,283 ZIP codes in this dataset. Within MT, it ranks 269 of 392.
Learn more
Two guides worth reading on 59004: zone vs. frost date, on why Zone 4b and Colstrip's frost date answer different questions, and the frost range, on how to read the range around Colstrip's dates instead of trusting one.