- Heat waves kill more people in the United States than all other weather-related disasters combined.
- More frequent and intense heat waves are likely because of human-caused climate change.
- An excessive heat warning means that some people can be seriously affected by heat if precautions are not taken.
Sure, it’s summer, and it’s supposed to be hot. But sometimes the heat can be extreme and dangerous for some people.
Heat waves are less exciting or dramatic than other natural disasters such as tornadoes, hurricanes, flooding or even thunderstorms, but they kill more people in the U.S. than all other weather-related disasters combined – causing hundreds of deaths each year, according to the National Weather Service.
Scientists say more frequent and intense heat waves are likely because of human-caused climate change.
Here’s all you need to know about excessive summertime heat and humidity.
What is the heat index?
“It’s not the heat, it’s the humidity.” That’s a partly valid phrase you may have heard in the summer, but it’s actually both, the weather service said. The heat index, also known as the apparent temperature, is what the temperature feels like to the human body when relative humidity is combined with the air temperature, according to the weather service.
“This has important considerations for the human body’s comfort. When the body gets too hot, it begins to perspire or sweat to cool itself off,” the weather service said. “If the perspiration is not able to evaporate, the body cannot regulate its temperature.”
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What is a heat wave? How does it impact us?
A heat wave is a period of unusually hot weather that typically lasts two or more days, according to the National Oceanic and Atmospheric Administration. To be considered a heat wave, the temperatures have to be outside the historical averages for a given area.
A couple of 95 degree summer days in Maine, for example, might be considered a heat wave, but a couple of 95 degree summer days in Death Valley would be pretty unremarkable, the weather service said.
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Extreme heat also impacts our infrastructure – from transportation to utilities to clean water and agriculture. High heat can deteriorate and buckle pavement, warp or buckle railway tracks and exceed certain types of aircraft operational limits. Electricity usage increases as air conditioning and refrigeration units in homes and offices work harder to keep indoors cooler.
What is a heat dome?
Extreme heat often results from a large area of high pressure, known as a “heat dome,” AccuWeather said. High-pressure atmospheric conditions combine with influences from La Niña, creating vast areas of sweltering heat that gets trapped under a “dome,” according to NOAA.
What is an excessive heat warning? What about a heat advisory?
An excessive heat warning is issued by the weather service within 12 hours of the onset of extremely dangerous heat conditions. The general rule of thumb for this warning is when the maximum heat index temperature is expected to be 105 degrees or higher for at least two days and nighttime air temperatures will not drop below 75 degrees; however, these criteria vary across the country, especially for areas not used to extreme heat conditions.
This is important because if you don’t take precautions immediately when conditions are extreme, you may become seriously ill or even die, the weather service warned.
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An excessive heat warning means that some people can be seriously affected by heat if precautions are not taken. Studies in Canada, Europe and the U.S. have indicated that mortality begins to increase exponentially as the heat increases or stays above a heat index of 104 degrees.
The weather service issues a heat advisory within 12 hours of the onset of extremely dangerous heat conditions.
The general rule of thumb for this advisory is when the maximum heat index temperature is expected to be 100 degrees or higher for at least 2 days, and nighttime air temperatures will not drop below 75 degrees; however, these criteria also vary across the country, especially for areas that are not used to dangerous heat conditions.