Dangerous heat wave looms for over 135 million next week from Chicago to Philadelphia

The first widespread heat wave of the year is about to unfold over the eastern and central United States with the AccuWeather RealFeel® Temperatures occasionally approaching the 100-degree mark.

A dangerous, widespread heat wave is predicted to unfold for millions across the Northeast, Midwest and parts of Canada next week with AccuWeather RealFeel® Temperatures even approaching the 100-degree Fahrenheit mark in some cities.

"The increased demand for cooling is going to be a problem here. This could have some impacts on the power grid," AccuWeather Chief Video Meteorologist Bernie Rayno said.

In the Midwest and Northeast, a heat wave is considered to be at least three days with a high temperature of at least 90 degrees, and for some areas, the mercury will exceed that benchmark for most or all of the week.

Chicago heat wave could rival worst of 2023

The AccuWeather HeatWave Counter and Severity Index™ puts a heat wave into historical context, describing the severity, intensity and duration of the extreme temperatures. The impending heat wave in Chicago is predicted to be "moderate," on par with the only heat wave in 2022, which lasted from June 14-16.

Hot conditions will start to build in Chicago on Sunday before the heat wave entrenches itself over the region with highs in the mid-90s through at least midweek. Dry weather will accompany the hot spell with no appreciable rain in the forecast.

Philadelphia heat wave could last 7 days

Philadelphia had an early taste of summertime heat with the mercury topping out at 90 degrees back on April 29, but the impending heat wave will be significantly hotter and longer. The temperature will climb into the mid-90s several days in a row, with the hottest conditions expected around midweek.

Rayno added that the streak of 90-degree days in the city could extend almost an entire week.

There won't be much relief from the heat after the sun sets either, as overnight lows will only fall into the mid-70s.

Over 135 million face 90-degree temperatures

According to AccuWeather figures, at least 135 million people across the eastern United States and parts of eastern Canada will experience a heat wave next week.

However, forecasters are concerned that the high pressure responsible for the heat could strengthen and expand, which would put more than 150 million at risk of a dangerous heat wave.

The peak of the heat wave for most of this zone is expected around the same time as the start of astronomical summer, which takes place on Thursday, June 20, at 4:50 p.m. EDT.

Paired with the strong sunshine, high humidity and other factors, the AccuWeather RealFeel® Temperature will likely be several degrees higher than the actual air temperature.

Experts recommend avoiding outdoor activities during the afternoon and evening hours, which is usually the hottest part of the day. People who must be outside are encouraged to drink plenty of water and take breaks to cool off in the shade.

Heat waves, on average, kill more Americans than any other type of severe weather such as tornadoes, hurricanes, floods and lightning.