San Mateo County Climate
San Mateo County, California
Avg Annual Temp
57.5°F
Annual Precip
25.4"
Annual Snowfall
0.0"
Extreme Heat Days
13.6
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Seasonal Overview
National Comparison
Climate Profile
About San Mateo County Weather
A Mild Mediterranean Climate Near the Coast
San Mateo's average annual temperature of 57.6°F is warmer than the national median. This reflects a stable, temperate climate that avoids the extreme fluctuations seen in the interior U.S.
Cooler Than the California Average
The county's 57.6°F average is slightly cooler than the California state average of 58.7°F. It ranks in the middle-to-lower tier of warmth among the state's 58 counties.
Moderate Rain Compared to Bay Area Neighbors
With 25.4 inches of annual precipitation, San Mateo is drier than Santa Cruz to the south. However, it receives more moisture than the 21.2 inches recorded in Santa Clara.
Temperate Summers and Frost-Free Winters
July temperatures average a mild 63.9°F, and the county sees only 14 days of extreme heat per year. Snow is non-existent, while winter averages remain comfortable at 51.1°F.
Layered Clothing and Minimal HVAC Needs
The marine influence means residents rarely need heavy heating or cooling systems. Focus on layered clothing to manage the transition from foggy mornings to sunny afternoons.
Frequently Asked Questions
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Data source: NOAA National Centers for Environmental Information (NCEI), U.S. Climate Normals 1991-2020.
Climate normals are 30-year averages of weather variables computed from 1991 to 2020. Station data is aggregated to county level using spatial averaging. Data is informational only — not a substitute for official National Weather Service forecasts or emergency weather warnings.