Weather forecasters warn of a prolonged and dangerous heat wave set to blanket large swaths of the U.S. this week into the Fourth of July holiday weekend, with temperatures possibly reaching significant highs and posing a risk to public health.
The National Weather Service said on Sunday that the “potentially historic” heat wave will cover most of the central to eastern U.S., where temperatures in the 90s and low 100s Fahrenheit, combined with high humidity, will lead to heat indices—the temperatures that the body actually feels and that includes the impact of humidity—of 105–110°F in several places.
Nightly lows are also not expected to provide much relief, the weather service added, with the bulb only projected to drop to the 70s.
Experts have long warned that the climate crisis is poised to make periods of dangerous, deadly high temperatures more frequent and intense. Just across the Atlantic, Europe is experiencing its own sweltering “heat dome” that has pushed temperatures to regional highs and caused hundreds of excessive heat-related deaths across the continent. And in March, a heat wave scorched the western U.S. to 108°F, a rarity so early in the year.
Extreme heat has been the deadliest form of extreme weather in the U.S., killing more people annually than any other weather hazard, like hurricanes or tornadoes. Here’s what to know.
Read More: How to Safely Lower Your Body Temperature In Extreme Heat
Which parts of the U.S. will feel the heat?
Extreme heat is forecast through July 4 across the lower Great Lakes, the mid-Atlantic, and the Mississippi and Ohio River valleys, with high heat persisting across parts of the eastern Plains, the Mississippi Valley, the mid-Atlantic, and the Southeast throughout the following week.
On the East Coast, the cities of New York, Philadelphia, Washington, and Baltimore are expected to feel the heat. High temperatures are also expected in the cities of Chicago, Indianapolis, St. Louis, and Detroit, as well as in southern cities like Dallas, Texas; Little Rock, Ark.; and Memphis, Tenn.
Parts of Illinois, Iowa, Kansas, Michigan, and Tennessee have also been issued extreme heat warnings.
What’s causing the heat wave?
Weather experts say a “heat dome” is driving the heat wave. Heat domes refer to a high-pressure area in the atmosphere that extends a few miles upwards and traps hot ocean air. Such domes can usually last for days or weeks and usually affect large areas.
“Sometimes the pattern in the summer just gets stagnant like this,” Bryan Putnam from the National Weather Service’s Weather Prediction Center told Fox News, adding that the humidity will compound the effect of the high temperatures on people.
Maps from the National Weather Service show several areas placed under Extreme Heat Risk. For heat-sensitive groups like the elderly and young children, this kind of temperature may be deadly, and health systems are likely to face strain from cases of heat-related illnesses.
Putnam said the level of heat will affect everyone, especially those who are not adequately hydrated or have no means of cooling down.
The weather service has advised areas under the Extreme Heat Risk category to strongly consider canceling outdoor activities, and for affected people to use cooling systems, to stay hydrated, and to stay in a cool place, including overnight.
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