Philly area under Heat Advisory Thursday, with heat index values up to 103; Code Orange declared due to poor air quality

The Philadelphia region is facing another summer heat wave.

A Heat Advisory will be in effect from 10 a.m. Thursday through 8 p.m. Friday, with heat index values up to 103 degrees possible.

The Heat Advisory will be in effect for the following counties:

Hot temperatures and high humidity may cause heat illnesses, the National Weather Service said.

Philly, suburbs under Code Orange due to poor air quality

Pennsylvania officials on Wednesday declared a Code Orange Air Quality Action Day for Ozone for the Philly region on Thursday. That includes Philadelphia, Bucks, Chester and Delaware counties.

The state Department of Environmental Protection cited mostly sunny skies, high temperatures in the mid- to upper-90s and light southwest winds as likely contributors to 8-hour average concentrations of ground-level ozone in the Code Orange range.

Ozone is formed from burning fossil fuels. Cars, trucks, power plants and industrial facilities contribute nitrogen oxides and volatile organic compounds which, when combined with sunlight, create smog, also known as ground-level ozone.

Under a Code Orange, air pollution concentrations may be unhealthy for vulnerable groups such as children, people with asthma, people with heart or lung disease and older adults.

Residents and businesses are also encouraged to reduce ozone air pollution by driving less, limiting engine idling and conserving electricity by setting air conditioning to a higher temperature and turning off lights not in use.

Residents are encouraged to visit AirNow.gov to check local conditions.

If you need a primer, here’s how to understand your air quality index.