Dangerous heat is spreading across the Plains and over the East Coast.  

HEAT WAVE WALLOPING SOUTHWEST CLAIMS 7 MORE LIVES IN PHOENIX AREA

Excessive heat expands eastward

Excessive heat expands eastward across the U.S. (Credit: Fox News)

Many big cities from Washington, D.C., to Boston are under a heat advisory, while an excessive heat warning is in effect for the New York City metro area, where the temperature will feel over 100 degrees with the humidity combined.  

New York City forecast heat index

The heat index forecast in New York City (Credit: Fox News)

Meanwhile, strong-to-severe thunderstorms will also be possible for parts of the Northeast and the upper Midwest, bringing the risk of large hail, damaging winds and isolated tornadoes.  

Heat alerts in the eastern U.S.

Heat alerts forecast through Friday night the eastern U.S. (Credit: Fox News)

The heavy rain potential could cause flash flooding in areas that have already received plenty of wet weather.  

Plains, Northeast storm threats

The threat of severe storms on Thursday across the Plains, Northeast (Credit: Fox News)

CLICK HERE TO GET THE FOX NEWS APP 

Northeast flood alerts

Flood alerts across the Northeast on Thursday (Credit: Fox News)

Finally, parts of the Southwest are also getting some rain with cloud cover as the monsoon season kicks in, and that’s helping bring down the temperatures for this region.