Chester, MT 59522 Frost Dates
Frost dates for Chester, MT, ZIP 59522
The last spring frost here typically falls around 05/24, about 269 days from today. The first fall frost typically arrives around 09/17, about 115 frost-free days later.
Zone 4a (-30 to -25°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 Chester, not a forecast for this year.
What to do before the first frost
Zone 4a around Chester has about 3 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 Chester's last frost
05/24 is the middle of 30 years of NOAA records, not a promise. Plant by 05/11 and you're betting against frost in roughly 9 years out of 10. 06/09 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Chester compares
Chester's growing season runs about 115 days, ranking 39,324 of 40,283 US ZIP codes measured here, longest to shortest. Within MT, it ranks 249 of 392.
Learn more
local microclimates explains what one yard in Chester can differ from the 59522 normal, and zone vs. frost date explains why Zone 4a and Chester's frost date answer different questions.