April 22, 2024

NWS Unveils New 'HeatRisk' Forecasts to Highlight Dangers of Extreme Heat

Heat kills more Americans every year than tornadoes, hurricanes, lightning, and flash floods combined. A new product released by the National Weather Service aims to cut down the tremendous number of heat-related illnesses and fatalities we see across the country every year.

HeatRisk is the culmination of a joint effort by the NWS and health experts with the Centers for Disease Control to increase awareness of the dangers of extreme heat throughout the U.S.

The new product is similar to the Winter Storm Severity Index in that it uses a five-category scale to relay the dangers posed by conditions on a particular day.

According to the NWS, forecasters will consider factors like:
  • The time of year
  • How far above normal temperatures are for that time of year
  • How long the unusual heat will stick around
  • Temperatures reaching thresholds known to cause heat-related illnesses
Those are important considerations when it comes to heat safety. A heat wave in May might warrant a higher rating as it may deliver a greater "shock to the system" (so to speak) than similar heat in August. Time, place, and duration all play a major role as well. A week of 90°F readings in Florida might not affect residents as much as a week of 90°F readings in Vermont.

HeatRisk will show up in products and on maps using a five-category scale ranging from 0 to 4, with "little to no risk" on the low end to "extreme impacts" on the high end. These categories are designed to quickly convey the severity of heat in the forecast for any particular area.

If you're in the red for "major impacts," for instance, it's going to be hot enough that fans won't effectively cool down indoor spaces, and anyone outdoors in the heat of the day—even healthy individuals—are at risk for heat-related illnesses.

Why this standardized scale matters

Excessive heat is a silent killer. A widespread heat wave can kill dozens and even hundreds of people without ever making the news. Elderly people, folks living with chronic conditions, and people working and living outdoors routinely succumb to heat exhaustion and life-threatening illnesses like heat stroke.

We're bombarded by alerts for tornadoes, hailstorms, hurricanes, and even wildfires. But heat—a deadlier threat than them all—routinely gets shrugged off. It's just summer, after all, what's the big deal?

This kind of a product is a long time coming. For years, we've relied on the heat index and the wet bulb globe temperature (WBGT) to measure the impacts of heat on the human body.

Meteorologists and medical scientists worked together to create the heat index to measure the combined impact of temperature and humidity on the human body. The NWS uses the heat index as a metric to issue heat advisories and excessive heat warnings, the thresholds for which are higher in areas like Phoenix or Miami than they are in cooler climates like Boston or Seattle. 

The wet bulb globe temperature (WBGT) goes a step further by factoring in more than just the temperature and humidity, including parameters like cloud cover, winds, and the sun angle to more accurately judge heat stress on the human body. The WBGT is especially useful for keeping athletes safe on hot days. 

Those two metrics often lead to confusion for the general public. Making matters worse is the widely believed lie that the heat index is "made up" for ratings (oh brother).

HeatRisk seeks to cast aside those ignorable digits in favor of an easy-to-understand scale that can help everyday folks use the forecast to stay safe, with the added benefit of alerting local officials and hospitals that they may need to provide relief and assistance to those who need it the most.

Right now, HeatRisk forecasts are still in the "experimental" stage. The NWS often introduces new products like this as experimental services that aren't used in everyday forecasting and decision-making.

You can provide feedback on the HeatRisk program directly to the NWS, and they'll use all the comments, concerns, and suggestions they receive to tweak the product before making it an official service.

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I graduated from the University of South Alabama in 2014 with a degree in political science and a minor in meteorology. I contribute to The Weather Network as a digital writer, and I've written for Forbes, the Washington Post's Capital Weather Gang, Popular Science, Mental Floss, and Gawker's The Vane. My latest book, The Skies Above, is now available. My first book, The Extreme Weather Survival Manual, arrived in October 2015.