Joliet, MT 59013 Frost Dates
Frost dates for Joliet, MT, ZIP 59013
Typically, the last spring freeze lands around 05/29, roughly 274 days out. The first fall frost typically arrives around 09/15, about 107 frost-free days later.
The USDA Plant Hardiness Zone Map puts Joliet in Zone 5a (-20 to -15°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 5a around Joliet 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.
Why 05/29 isn't a guarantee
05/29 is the middle of 30 years of NOAA records, not a promise. Plant by 05/14 and you're betting against frost in roughly 9 years out of 10. 06/17 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Joliet compares
About 107 days separate Joliet's last and first frost, putting it 39,567 of 40,283 ZIP codes nationally. Within MT, it ranks 285 of 392.
Learn more
zone vs. frost date explains why Zone 5a and Joliet's frost date answer different questions, and the frost range explains how to read the range around Joliet's dates instead of trusting one.