Underwood, IA 51576 Frost Dates
51576, near Underwood, IA: the frost window
Typically, the last spring freeze lands around 04/18, roughly 233 days out. Fall's first freeze usually shows up around 10/21, roughly 185 days after the last spring frost.
Underwood sits in USDA Zone 5b (-15 to -10°F average annual minimum). The dates above are NOAA's 1991-2020 normal at the nearest reporting station, a 30-year average, not a forecast.
Stretching the season past the first frost
Underwood's growing season runs out in roughly 8 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 Underwood's last frost
04/18 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/05 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 04/30 and only about 1 year in 10 sees frost after that.
Underwood against the rest of the dataset
Underwood's growing season runs about 185 days, ranking 23,241 of 40,283 US ZIP codes measured here, longest to shortest. Within IA, it ranks 43 of 1,042.
Learn more
Two guides worth reading on 51576: zone vs. frost date, on why Zone 5b and Underwood's frost date answer different questions, and the frost range, on how to read the range around Underwood's dates instead of trusting one.