Today | Weather | Saturday, September 19, 2026

Weather in San Mateo, California

01:47 AM
Now
Cloudy Weather
57° F
Feels Like 55°
Precipitation 0 %
Wind 6 mph
Humidity 95 %
Today
Cloudy Weather
Day 75°
Night 57°
Precipitation 1 %
Wind 8 mph
UV Index (0 - 11+) 5

San Mateo Weather Forecast Updated

10 minutes ago
Last updated on
Weather Forecast History
Last Year's Weather on This Day (September 19, 2025)
Cloudy Night

Day

75°

Night

61°

Wind

6 mph

Precipitation

2 %

Air Quality in San Mateo

NOW
41 AQI
Good air quality Dominant pollutant: O3

Pollutant Concentrations:

PM2.5 6.67 µg/m³
PM10 23.65 µg/m³
O3 0.044 ppm
NO2 0.4 ppb
SO2 0.3 ppb
CO 0.13 ppm
NH3 0 µg/m³
NO 0 µg/m³
PM2.5 – Fine particles <2.5μm
PM10 – Inhalable particles <10μm
O3 – Ozone
NO2 – Nitrogen dioxide
SO2 – Sulfur dioxide
CO – Carbon monoxide
NH3 – Ammonia
NO – Nitric oxide

Health Recommendations:

Air quality is considered satisfactory, and air pollution poses little or no risk.

Show raw pollutant concentrations (µg/m³)
PM2.56.67 µg/m³
PM1023.65 µg/m³
O386.35 µg/m³
NO20.71 µg/m³
SO20.88 µg/m³
CO150.69 µg/m³
NH30 µg/m³
NO0 µg/m³