Missoula, MT 59851 Frost Dates
Frost dates for Missoula, MT, ZIP 59851
Typically, the last spring freeze lands around 05/10, roughly 255 days out. The first fall frost typically arrives around 10/01, about 143 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 Missoula, not a forecast for this year.
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.
The actual range around Missoula's last frost
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 36,491 of 40,283 ZIP codes in this dataset. Within MT, it ranks 43 of 392.
Learn more
zone vs. frost date explains why Zone 5b and Missoula's frost date answer different questions, and the frost range explains how to read the range around Missoula's dates instead of trusting one.