Once the Philadelphia region gets past the heat wave, unstable air returns, and the storm door will open through the weekend.

Extreme heat has increasingly proven fatal in the last few decades as sweltering temperatures have become more common. In 2024, a study published in the Journal of the American Medical Association identified a 117% increase in heat-related deaths from 1999 to 2023, including a steady uptick since 2016.

It's oppressive outside today in Pennsylvania, as heat indices may near 110 degrees. When is relief on the way? Here's the forecast, heat maps, more.