Shelby, MT 59461 Frost Dates
59461, near Shelby, MT: the frost window
Typically, the last spring freeze lands around 05/23, roughly 268 days out. Fall's first freeze usually shows up around 09/16, roughly 115 days after the last spring frost.
Shelby sits in USDA Zone 4a (-30 to -25°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
Shelby'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.
How much risk comes with planting early here
05/23 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/11 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 06/06 and only about 1 year in 10 sees frost after that.
Shelby against the rest of the dataset
At roughly 115 frost-free days, Shelby places 39,312 of 40,283 ZIP codes in this dataset. Within MT, it ranks 244 of 392.
Learn more
Two guides worth reading on 59461: zone vs. frost date, on why Zone 4a and Shelby's frost date answer different questions, and the frost range, on how to read the range around Shelby's dates instead of trusting one.