San Mateo County, CA: Current UV Index and Hourly Forecast

As of 9:21 AM PDT on September 18, 2025, all 33 cities in San Mateo County, CA in our database have a UV Index reading of Low. The city with the highest UV Index reading right now is San Mateo, CA with a reading of 1.1.

Over the next 24 hours, the highest UV Index reading in San Mateo County, CA is expected to be 6.7 in Portola Valley between 1:00 PM - 2:00 PM PDT today.

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UV Index Risk Levels
Range0 - 23 - 56 - 78 - 1011+
Color
RiskLowModerateHighVery HighExtreme
UV Index in San Mateo County, CA as of 9:21 AM PDT, September 18, 2025

Current UV Index in Cities in San Mateo County, CA

9:21 AM PDT, September 18, 2025