Billings, MT 59103 Frost Dates
Billings, MT: when does the frost end?
Typically, the last spring freeze lands around 05/12, roughly 257 days out. Fall's first freeze usually shows up around 09/25, roughly 136 days after the last spring frost.
Zone 5a (-20 to -15°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 Billings, not a forecast for this year.
Stretching the season past the first frost
With roughly 4 weeks until Billings's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
Why 05/12 isn't a guarantee
05/12 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/30 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/26 and only about 1 year in 10 sees frost after that.
Billings against the rest of the dataset
About 136 days separate Billings's last and first frost, putting it 37,613 of 40,283 ZIP codes nationally. Within MT, it ranks 84 of 392.
Learn more
Before leaning on 59103's figures: local microclimates explains what one yard in Billings can differ from the 59103 normal, while zone vs. frost date explains why Zone 5a and Billings's frost date answer different questions.