Three Forks, MT 59735 Frost Dates
Frost dates for Three Forks, MT, ZIP 59735
Typically, the last spring freeze lands around 04/30, roughly 245 days out. The first fall frost typically arrives around 10/10, about 162 frost-free days later.
Three Forks 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.
What to do before the first frost
Zone 5a around Three Forks has about 6 weeks left before the first fall frost — that's the usual window to get a cold frame up if you want to keep harvesting past it.
Why 04/30 isn't a guarantee
04/30 is the middle of 30 years of NOAA records, not a promise. Plant by 04/15 and you're betting against frost in roughly 9 years out of 10. 05/14 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Three Forks compares
At roughly 162 frost-free days, Three Forks places 31,759 of 40,283 ZIP codes in this dataset. Within MT, it ranks 6 of 392.
Learn more
zone vs. frost date explains why Zone 5a and Three Forks's frost date answer different questions, and the frost range explains how to read the range around Three Forks's dates instead of trusting one.