Millions from the Midwest to the Northeast prepare for a weeklong heat wave

A boy plays in a splash pad at Riverview Park on June 5 in Mesa, Ariz. Justin Sullivan/Getty Images hide caption

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A sweltering heat wave is bearing down on a large swath of the U.S., creating potentially dangerous conditions for millions of people in multiple states.

Meteorologists say the stifling temperatures could break daily record highs and last throughout the week in what the National Weather Service has described as the first major heat wave of the summer.

“The duration of this heat wave is notable and potentially the longest experienced in decades for some locations,” the NWS said in a post on the social media platform X.

Scorching temperatures are beginning to affect the Midwest on Sunday, and over the next few days will reach much of the Great Lakes, Northeast and Mid-Atlantic. Those searing conditions are expected to last all week.

Major cities at risk for extreme heat include New York, Chicago, Philadelphia and Indianapolis.

The local heat index — what the weather outside feels like when you account for both the air temperature and relative humidity — could reach 105 degrees in some places, the NWS said. Highs in the 90s could be seen as far north as Vermont and New Hampshire.

At the same time, overnight temperatures dipping into the mid-70s in many metropolitan areas may offer only minor relief — if any at all — to people without reliable cooling.

Though it’s the country’s first major heat wave of the year, such extreme weather is becoming more common and intense with climate change.

The temperature in Chicago on Sunday was slated to rise as high as 93 and climb even higher on Monday. Detroit was preparing for “dangerously hot conditions” all week, with possible peak heat indices as high as 100 degrees.

The extreme weather arrived just after a heat dome stifled much of the western and southwestern U.S. earlier this month, sending temperatures over 100 and putting millions of Americans under heat warnings.

How to stay safe in the heat

Health officials are urging people to take extra precautions as temperatures soar, since extreme heat can harm your health. According to the NWS, heat is one of the leading weather-related causes of death in the U.S.

Those most at risk for heat-related illness include infants and young children, pregnant women, older adults and people with chronic medical conditions.

People should be on the lookout for signs of heat exhaustion and heat stroke, two distinct affiliations caused by high temperatures.

According to the Centers for Disease Control and Prevention, symptoms of heat exhaustion include headache, nausea, dizziness, sweating and thirst. Sufferers should move to a cooler place, take sips of water and cool themselves down by removing unnecessary clothing or using cold compresses.

Heat stroke, which is more serious, can cause confusion, loss of consciousness, profuse sweating and a very high body temperature.

If you suspect someone has heat stroke, you should call 911 and move the person to a cooler place, but don’t give them anything to drink.