Today | Weather | Wednesday, May 20, 2026
Active Weather Warnings

Weather in Costa Mesa, California

01:51 PM
Now
Cloudy Weather
77° F
Feels Like 82°
Precipitation 0 %
Wind 9 mph
UV Index (0 - 11+) 10
Humidity 47 %
Today
Sunny Weather
Day 79°
Night 61°
Precipitation 1 %
Wind 7 mph
UV Index (0 - 11+) 11

Warning: Extreme UV Index Today: 11

Overexposure to the sun's harmful UV rays can cause sunburn and increase the risk of developing skin cancer, including melanoma. Protect yourself by wearing clothing that covers your skin, sunglasses, and a hat. Apply a broad-spectrum sunscreen with an SPF of 30 or higher every two hours, even on cloudy days. Minimize direct sun exposure during peak hours (10 AM to 4 PM) to reduce the risk.

Costa Mesa Weather Forecast Updated

Last updated on
Weather Forecast History
Last Year's Weather on This Day (May 20, 2025)
Sunny Weather

Day

77°

Night

59°

Wind

6 mph

UV Index

11

Precipitation

0 %

Air Quality in Costa Mesa

NOW
48 AQI
Good air quality Dominant pollutant: O3

Pollutant Concentrations:

PM2.5 9.87 µg/m³
PM10 22.64 µg/m³
O3 0.052 ppm
NO2 0.2 ppb
SO2 0.3 ppb
CO 0.11 ppm
NH3 0 µg/m³
NO 0.06 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)
PM2.59.87 µg/m³
PM1022.64 µg/m³
O3102.22 µg/m³
NO20.3 µg/m³
SO20.69 µg/m³
CO124.64 µg/m³
NH30 µg/m³
NO0.06 µg/m³

Weather Alerts and Warnings for Costa Mesa

Air Quality Alert

Air Quality Alert issued May 19 at 11:05PM PDT by NWS San Diego CA
May 19, 11:05 PM May 20, 4:30 PM
Updated: May 20, 12:29 PM Source: NWS Alert