Kalispell, MT 59904 Frost Dates
59904, near Kalispell, MT: the frost window
Around 05/31 is the usual last spring frost, about 276 days away. Fall's first freeze usually shows up around 09/10, roughly 100 days after the last spring frost.
Kalispell sits in USDA Zone 5b (-15 to -10°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
Kalispell's growing season runs out in roughly 2 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
Why 05/31 isn't a guarantee
05/31 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/13 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 06/22 and only about 1 year in 10 sees frost after that.
Kalispell against the rest of the dataset
Kalispell's growing season runs about 100 days, ranking 39,707 of 40,283 US ZIP codes measured here, longest to shortest. Within MT, it ranks 308 of 392.
Learn more
Two guides worth reading on 59904: local microclimates, on what one yard in Kalispell can differ from the 59904 normal, and zone vs. frost date, on why Zone 5b and Kalispell's frost date answer different questions.