Upcoming heat wave isn’t “just summer.” Heat is a prolific killer.

The first major heat wave of the season is on the way for a large swath of the eastern United States, with a prolonged stretch of daytime high temperatures in the 90s with heat indices in the 100s likely.

Every time we get a big heat wave, social media lights up with that classic line: “It’s called summer.”

Always typed with the sneering smugness of a seventh grader, that three-word phrase is a catch-all to wave away any concern about an upcoming spell of dangerously hot temperatures.

Heat is deadly. It’s always been deadly. Lots and lots of people died “back in the day” during heat waves. Lots and lots of people still die during heat waves. You just don’t hear as much about it because their deaths weren’t caused by dramatic winds or rushing waters. 

Extreme heat caused nearly half of all weather-related fatalities between 2014 and 2024—often surpassing the tolls exacted by tornado outbreaks, major hurricane landfalls, and devastating flash flood events.

Heat waves exact large human cost because of humidity, hot nights, and longevity. 

Humidity: Sweat cools off our bodies through evaporative cooling—water absorbs heat when it evaporates from liquid to gas. This process pulls heat from our skin to cool our body temperature on a hot day. Excess moisture in the air interferes with this process by preventing sweat from evaporating efficiently, even when you have fans running. The heat index accounts for the combined stress that heat and humidity place on your body.

Hot nights: People who live without air conditioning rely on cooler nighttime temperatures to provide their bodies relief from a hot day. Hot days and elevated nighttime temperatures—alongside smothering humidity—robs these folks of the ability to cool off at night. 

Longevity: The compounding effects of stifling hot days and steamy nights takes a significant toll on vulnerable people. Those without access to air conditioning, folks working outdoors, and chronically ill individuals are highly susceptible to heat-related illnesses such as heat exhaustion and heat stroke.

A classic summertime heat event will build east of the Rockies heading into this weekend.

We’ll see a large and strong upper-level ridge develop and move toward the Ohio Valley on Saturday, lingering over the eastern half of the country well into next week. 

Air sinks beneath ridges, warming up and drying out as it descends toward the ground. Very strong and stubborn ridges of high pressure like this can trigger a feedback cycle that compounds the effects of heat and humidity for days on end. Meteorologists sometimes like to call this a “heat dome.” 

As a result, extreme heat is likely to build over a vast swath of the country beginning this weekend. The above graphic shows the National Weather Service’s experimental “HeatRisk” product, which conveys the potential danger of predicted heat. Communities in the “major impacts” and “extreme impacts” zones could see conditions that may threaten the health of even physically fit individuals. 

Widespread heat alerts are likely.

It only takes heat index values or air temperatures up around 100°F to trigger heat advisories across much of the northern United States. Remember, the impacts of heat are relative. Folks in the south are more acclimated to muggy heat than folks up north, so lower temperatures can have a higher impact in, say, Toledo than Mobile.

Get ready for a long and dangerously hot stretch of weather heading into next week. Heat is no joke—and don’t let the naysayers convince you otherwise.

---