Westport, SD 57426 Frost Dates
57426, near Westport, SD: the frost window
Around 05/09 is the usual last spring frost, about 254 days away. Fall's first freeze usually shows up around 09/26, roughly 139 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Westport in Zone 4a (-30 to -25°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
Stretching the season past the first frost
Westport's growing season runs out in roughly 4 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
The actual range around Westport's last frost
05/09 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/27 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/22 and only about 1 year in 10 sees frost after that.
Westport against the rest of the dataset
Westport's growing season runs about 139 days, ranking 37,307 of 40,283 US ZIP codes measured here, longest to shortest. Within SD, it ranks 325 of 378.
Learn more
Two guides worth reading on 57426: zone vs. frost date, on why Zone 4a and Westport's frost date answer different questions, and the frost range, on how to read the range around Westport's dates instead of trusting one.