Thompson Falls, MT 59873 Frost Dates
Frost dates for Thompson Falls, MT, ZIP 59873
Typically, the last spring freeze lands around 05/07, roughly 252 days out. The first fall frost typically arrives around 10/04, about 150 frost-free days later.
The USDA Plant Hardiness Zone Map puts Thompson Falls in Zone 6a (-10 to -5°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
What to do before the first frost
Zone 6a around Thompson Falls has about 5 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 05/07 isn't a guarantee
05/07 is the middle of 30 years of NOAA records, not a promise. Plant by 04/25 and you're betting against frost in roughly 9 years out of 10. 05/19 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Thompson Falls compares
Thompson Falls's growing season runs about 150 days, ranking 35,324 of 40,283 US ZIP codes measured here, longest to shortest. Within MT, it ranks 22 of 392.
Learn more
the frost range explains how to read the range around Thompson Falls's dates instead of trusting one, and local microclimates explains what one yard in Thompson Falls can differ from the 59873 normal.