Lewistown, MT 59457 Frost Dates
59457, near Lewistown, MT: the frost window
Around 05/23 is the usual last spring frost, about 268 days away. Fall's first freeze usually shows up around 09/21, roughly 119 days after the last spring frost.
Lewistown 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
Lewistown'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 Lewistown's last frost
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 06/08 and only about 1 year in 10 sees frost after that.
Lewistown against the rest of the dataset
Lewistown's growing season runs about 119 days, ranking 39,137 of 40,283 US ZIP codes measured here, longest to shortest. Within MT, it ranks 220 of 392.
Learn more
Two guides worth reading on 59457: local microclimates, on what one yard in Lewistown can differ from the 59457 normal, and zone vs. frost date, on why Zone 4b and Lewistown's frost date answer different questions.