A "Code Orange" air quality alert is in effect Wednesday, meaning pollution levels will be unhealthy for some people.

High pressure is forecast over the region, with calm winds and abundant sunshine allowing levels of ozone and particulate matter to build. Ozone is a gas that is important in upper levels of the atmosphere but is a harmful byproduct of fossil fuel exhaust close to the ground.

Conditions are forecast to be unhealthy for sensitive groups, including children, the elderly, and those with heart or lung conditions.

One more day of heat and humidity is forecast. Highs are forecast in the upper 80s, with the heat index expected around 90 degrees.

But starting Thursday, a cold front is forecast to clear out the air pollution, heat and humidity. Highs are forecast closer to 80 degrees through the weekend, with fall-like low levels of moisture in the air.