'It's Boiling': Extreme Heat Grips US with Dangerous, Record-Breaking Temperatures 

The calendar says June, but the hot temperatures feel more like deep summer as extreme heat grips the country.

"It's boiling. It feels like over 100 degrees out of here. It's very hot," said Tiffany Murray, who recently visited Philadelphia. 

In New York, temperatures reached nearly 100 degrees on Monday, the hottest since 1888.

And in Baltimore, MD, humidity made it feel like 113 degrees. 

A phenomenon known as a heat dome, a large area of high pressure in the upper atmosphere that traps heat and humidity, is causing the extreme temperatures.

Most of the northeastern part of the country, from Minnesota to Maine, is under some type of heat advisory. 

In Patterson, New Jersey, more than 160 people attending graduation ceremonies were treated for heat-related illnesses.

In Philadelphia, power outages caused by the strain on the power grid stranded people on a subway for more than an hour with no air conditioning.

And in some cities, the high heat is buckling roads and causing problems for drivers.

As the high temperatures continue, doctors warn to look for signs of heat stroke like if someone stops sweating and they're confused or slur their speech.

"Get to a hospital," said Dr. Marc Grossman, EMS Medical Director, HCA England. "Get to treatment very quickly because you need to be cooled down before your brain actually literally starts cooking."

"We have to drink plenty of fluids and try to stay, try to go indoors where there's air conditioning to get out of the heat and humidity at various times in the day," said Alan Bernstein, a resident from the suburbs of Philadelphia.

Meanwhile, meteorologists say the dangerous heat will continue through at least Wednesday.