Atherton, CA 94027 Frost Dates
94027, near Atherton, CA: the frost window
Typically, the last spring freeze lands around 01/17, roughly 142 days out. Fall's first freeze usually shows up around 12/12, roughly 333 days after the last spring frost.
Atherton sits in USDA Zone 9b (25 to 30°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
Atherton's growing season runs out in roughly 15 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
How much risk comes with planting early here
01/17 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 02/16 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 12/20 and only about 1 year in 10 sees frost after that.
Atherton against the rest of the dataset
At roughly 333 frost-free days, Atherton places 2,846 of 40,283 ZIP codes in this dataset. Within CA, it ranks 1,292 of 2,555.
Learn more
Two guides worth reading on 94027: zone vs. frost date, on why Zone 9b and Atherton's frost date answer different questions, and the frost range, on how to read the range around Atherton's dates instead of trusting one.