MILLIONS of Americans are set to face searing temperatures as a phenomenon that’s known as a heat dome covers vast swathes of the country. 

At least 150 million people are under heat warnings, with the temperatures in some cities threatening to reach three figures.

A heat dome is formed when a large area of high pressure traps heat, which then forces temperatures to rise.

Experts at the National Oceanic and Atmospheric Administration have warned that heat domes can blanket a region for weeks.

And, a map produced by the Environmental Protection Agency has revealed where the sun’s rays are usually strongest for this time of year.

Experts have warned how heatstroke can set in in just 15 minutes.

The UV Index ranges from one to 13, with states like Florida, parts of Texas, as well as southern Louisiana, Mississippi, and Georgia averaging between 10 and 11 in June.

This also applies for parts of California, Nevada, and northwestern Arizona.

An index of 10 to 11 means there is an extreme risk of sunburn.

Americans are warned to be careful outdoors, wear protective clothes, and use a minimum of SPF-15 sunscreen.

The eastern US will see an extremely dangerous heatwave especially during the early part of this week, according to the National Weather Service.

Forecasters have warned that temperature records are expected to be shattered.

Meanwhile, those in cities such as Washington DC and Philadelphia have been warned to expect significant heat impacts.

On Monday, temperatures in Raleigh, North Carolina, could reach 100F, while in Detroit, Louisville, and Memphis, the mercury could top 95F.

Temperatures of more than 90F are expected across Texas, Tennessee, and south Florida.

In New York, thermometers could hit 100F on Tuesday – with temperatures more than 10 degrees higher than normal. 

Boston and Atlanta are among the cities that could see temperatures of more than 95F.

Over the course of the weekend, heat indexes in Chicago hit 103F, while in Madison, Wisconsin, an index of 101F was recorded.

Beachgoers wasted no time enjoying the warm weather by flocking to a beach on the Lake Michigan shoreline.

While, those decided to cool off in the water by floating inside rubber rings.

Children rushed to drench their faces with water in fountains, while others cooled their faces by using sprinkler machines in the city.

Meanwhile, in New York, pictures showed one child cooling down in a pond fountain, while parks were packed with sunbathers.

Some sought shelter under umbrellas as they tried to shield themselves from the sun. 

But, it’s not just searing temperatures that Americans will have to grapple with. 

Forecasters have warned that it will be muggy and uncomfortable due to high dew points.

A figure under 55 is associated with comfortable conditions, but along the East Coast, the dew point is set to be above 70. 

STATE OF EMERGENCY

The extreme heat has prompted officials to issue state of emergency orders.

On Sunday, New York Governor, Kathy Hochul, declared a state of emergency that impacts 32 counties.

Eric Adams, the New York City mayor, warned the first heatwave of the year has arrived. 

“Summer in the city is here — and so is our first heat wave of the year,” he said.

“This intense heat won’t just be uncomfortable and stifling—it will be severe and pose a danger to those spending long periods outdoors.

“This week’s heat wave could be deadly and life threatening if you are not prepared.”

Officials have recommended Americans to use air conditioning, but also suggested they should head to cooling centers if they do not have access.

“As temperatures climb to almost 100 degrees this week, we strongly advise all New Yorkers to treat the heat with seriousness,” stated Zach Iscol, commissioner of New York Emergency Management.

A heat emergency is also in place across Boston and this will remain in force until Tuesday.

Temperatures in the city could feel like 100F.

Michelle Wu, the city’s mayor, revealed swimming pools and splash pads are open, while medical officials have warned they typically face a 10 to 15% increase in 911 calls.

New York isn’t just grappling with high temperatures; thunderstorms and tornadoes have also battered the state.

Twins Emily and Kenni Bisson, six, died after a tree collapsed onto their home in a New York hamlet.

Shelly Johnson, 50, died after a tree collapsed on her home, officials said.

Power outages have also been reported – with around 30,000 people across New York suffering from blackouts as of Monday morning, according to PowerOutage US figures.