Alberton, MT 59820 Frost Dates
Frost dates for Alberton, MT, ZIP 59820
The last spring frost here typically falls around 05/18, about 263 days from today. The first fall frost typically arrives around 09/25, about 126 frost-free days later.
Alberton 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.
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.
The actual range around Alberton's last frost
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 38,707 of 40,283 ZIP codes nationally. Within MT, it ranks 161 of 392.
Learn more
local microclimates explains what one yard in Alberton can differ from the 59820 normal, and zone vs. frost date explains why Zone 5b and Alberton's frost date answer different questions.