Missoula, MT 59802 Frost Dates
Frost dates for Missoula, MT, ZIP 59802
Around 05/10 is the usual last spring frost, about 255 days away. The first fall frost typically arrives around 10/01, about 143 frost-free days later.
Missoula 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 Missoula 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.
How much risk comes with planting early here
05/10 is the middle of 30 years of NOAA records, not a promise. Plant by 04/27 and you're betting against frost in roughly 9 years out of 10. 05/28 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Missoula compares
At roughly 143 frost-free days, Missoula places 36,488 of 40,283 ZIP codes in this dataset. Within MT, it ranks 40 of 392.
Learn more
local microclimates explains what one yard in Missoula can differ from the 59802 normal, and zone vs. frost date explains why Zone 5b and Missoula's frost date answer different questions.