Authorities continue to warn of harmful air quality as smoke drifts into Santa Clara Valley from numerous wildfires burning in the Santa Cruz Mountains and beyond.

Residents likely woke up this morning with their vehicles covered in ashes and enough smoke filling the air to obstruct visibility and complicate breathing. The River Fire, burning south of Salinas, grew from about 4,000 acres Monday afternoon to more than 10,000 acres this morning, according to Cal Fire officials.

Firefighters are also fighting the SCU Lightning Complex Fire, which consists of numerous wildfires throughout the Bay Area that have collectively burned more than 85,000 acres as of today. One of these fires is burning east of Morgan Hill and Gilroy in Henry W. Coe State Park, and another is ablaze in the Santa Cruz Mountains.

Thousands of residents have been evacuated.

The fires have caused smoke pollution throughout the region, and residents are advised to stay indoors due to the poor air quality. The Bay Area Air Quality Management District (BAAQMD) rates Wednesday’s air quality index for Santa Clara County at 107, which falls in the category “Unhealthy for Sensitive Groups.”

The air quality forecast for Thursday shows the AQI rating will worsen to 157 in the South Bay, according to the BAAQMD website.

The Monterey Bay Air Resources District rated the air quality for San Benito County in the generally “Unhealthy” range.

“An unhealthy level is defined as some members of the general may experience health effects: members of sensitive groups may experience more serious health effects,” according to a press release from San Benito County. “If you see smoke in the air or smell smoke, then there can be risks to your health.”

If you or someone you know is struggling to breathe, contact a health care provider for advice. Air quality can change quickly as fires progress and wind changes direction. For real-time air quality reports go to mbard.org/airquality and cdc.gov/features/wildfires.