San Mateo, CA 94401 Frost Dates
94401, near San Mateo, CA: the frost window
Typically, the last spring freeze lands around 12/29, roughly 123 days out. Fall's first freeze usually shows up around 12/26, roughly 365 days after the last spring frost.
Zone 10a (30 to 35°F average annual minimum) comes from the USDA Plant Hardiness Zone Map; the frost dates above are the 1991-2020 normal at the nearest reporting NOAA station for San Mateo, not a forecast for this year.
Stretching the season past the first frost
San Mateo's growing season runs out in roughly 17 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
12/29 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 01/13 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 12/11 and only about 1 year in 10 sees frost after that.
San Mateo against the rest of the dataset
At roughly 365 frost-free days, San Mateo places 495 of 40,283 ZIP codes in this dataset. Within CA, it ranks 211 of 2,555.
Learn more
Two guides worth reading on 94401: zone vs. frost date, on why Zone 10a and San Mateo's frost date answer different questions, and the frost range, on how to read the range around San Mateo's dates instead of trusting one.