Hysham, MT 59076 Frost Dates
Frost dates for Hysham, MT, ZIP 59076
Around 05/10 is the usual last spring frost, about 255 days away. The first fall frost typically arrives around 09/29, about 141 frost-free days later.
Zone 4b (-25 to -20°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 Hysham, not a forecast for this year.
What to do before the first frost
Zone 4b around Hysham 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 05/10 isn't a guarantee
05/10 is the middle of 30 years of NOAA records, not a promise. Plant by 04/28 and you're betting against frost in roughly 9 years out of 10. 05/22 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Hysham compares
At roughly 141 frost-free days, Hysham places 36,989 of 40,283 ZIP codes in this dataset. Within MT, it ranks 64 of 392.
Learn more
the frost range explains how to read the range around Hysham's dates instead of trusting one, and local microclimates explains what one yard in Hysham can differ from the 59076 normal.