Isabel, SD 57633 Frost Dates
Isabel, SD: when does the frost end?
Around 05/11 is the usual last spring frost, about 256 days away. Fall's first freeze usually shows up around 09/30, roughly 140 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Isabel in Zone 4b (-25 to -20°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
With roughly 5 weeks until Isabel's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
The actual range around Isabel's last frost
05/11 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 05/24 and only about 1 year in 10 sees frost after that.
Isabel against the rest of the dataset
About 140 days separate Isabel's last and first frost, putting it 37,186 of 40,283 ZIP codes nationally. Within SD, it ranks 310 of 378.
Learn more
Before leaning on 57633's figures: local microclimates explains what one yard in Isabel can differ from the 57633 normal, while zone vs. frost date explains why Zone 4b and Isabel's frost date answer different questions.