Here's how the National Weather Service analyzes dangerous heat
Going beyond the typical heat forecast
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When people think of dangerous weather, they usually think of tornadoes, hurricanes or floods, not heat. But every year, extreme heat is one of the deadliest weather hazards in the United States.
That’s why the National Weather Service created HeatRisk, a tool designed to show when heat goes from uncomfortable to dangerous, and who is most at risk. Let’s take a closer look at how it works.
How does HeatRisk work?
HeatRisk uses a color-coded scale that considers factors including daytime highs, warm overnight temperatures, humidity, duration of the heat, local climate and even how accustomed people are to the heat in a particular area.
Think of it like a stress meter for the human body.
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At the lower end, green and yellow levels indicate little to minor concern. As the colors climb into orange, red and magenta, the risks increase especially for people without air conditioning, outdoor workers, older adults and anyone not acclimated to the heat.
Magenta, the highest category, is reserved for rare and prolonged extreme heat events where even overnight temperatures offer little relief. Those are the types of heat waves that can strain hospitals, infrastructure, and entire communities.
Why HeatRisk matters
One of the biggest challenges with heat safety is that dangerous heat is often underestimated. People may assume they are safe because temperatures are “normal for summer,” even when prolonged heat can still place stress on the body.
For example, a temperature of 95 degrees in Minnesota early in June may pose a greater health risk than the same temperature in Arizona because people are less acclimated to extreme heat. HeatRisk accounts for those regional differences.
The HeatRisk map for Wednesday highlights widespread moderate to major heat risk across parts of the Northern Plains and Upper Midwest.
Large areas of the Dakotas into Minnesota are shaded orange, signaling moderate heat impacts, while portions of northern Montana and northwestern North Dakota are shaded red, indicating major heat risk.
What makes this HeatRisk map especially useful is that it focuses on how the heat may affect people by taking into account how unusual the temperatures are for late May, how long the heat lasts and whether overnight conditions provide relief.
Visit NOAA’s HeatRisk website for more information.
