Westport, SD 57481 Frost Dates
Frost dates for Westport, SD, ZIP 57481
Typically, the last spring freeze lands around 05/09, roughly 254 days out. The first fall frost typically arrives around 09/28, about 141 frost-free days later.
The USDA Plant Hardiness Zone Map puts Westport in Zone 4b (-25 to -20°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 4b around Westport has about 4 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
05/09 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. 05/21 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Westport compares
About 141 days separate Westport's last and first frost, putting it 37,010 of 40,283 ZIP codes nationally. Within SD, it ranks 305 of 378.
Learn more
local microclimates explains what one yard in Westport can differ from the 57481 normal, and zone vs. frost date explains why Zone 4b and Westport's frost date answer different questions.