Alberton, MT 59846 Frost Dates
Frost dates for Alberton, MT, ZIP 59846
Typically, the last spring freeze lands around 05/18, roughly 263 days out. The first fall frost typically arrives around 09/25, about 126 frost-free days later.
Zone 5b (-15 to -10°F average annual minimum) comes from the USDA Plant Hardiness Zone Map; the frost dates above are the 1991-2020 normal at the nearest reporting NOAA station for Alberton, not a forecast for this year.
What to do before the first frost
Zone 5b around Alberton has about 4 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.
How much risk comes with planting early here
05/18 is the middle of 30 years of NOAA records, not a promise. Plant by 05/05 and you're betting against frost in roughly 9 years out of 10. 06/06 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Alberton compares
About 126 days separate Alberton's last and first frost, putting it 38,709 of 40,283 ZIP codes nationally. Within MT, it ranks 163 of 392.
Learn more
local microclimates explains what one yard in Alberton can differ from the 59846 normal, and zone vs. frost date explains why Zone 5b and Alberton's frost date answer different questions.