Eureka, MT 59933 Frost Dates
59933, near Eureka, MT: the frost window
Typically, the last spring freeze lands around 05/16, roughly 261 days out. Fall's first freeze usually shows up around 09/18, roughly 121 days after the last spring frost.
Eureka sits in USDA Zone 5a (-20 to -15°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
Eureka'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
05/16 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/03 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 06/03 and only about 1 year in 10 sees frost after that.
Eureka against the rest of the dataset
Eureka's growing season runs about 121 days, ranking 39,018 of 40,283 US ZIP codes measured here, longest to shortest. Within MT, it ranks 207 of 392.
Learn more
Two guides worth reading on 59933: the frost range, on how to read the range around Eureka's dates instead of trusting one, and local microclimates, on what one yard in Eureka can differ from the 59933 normal.