Dangerous temperatures are once again the biggest weather headline across the U.S. on Tuesday, with more than 100 million people under heat advisories from the Plains up into the Northeast.  

HERE ARE THE HEALTH RISKS OF EXTREME HEAT

Many big cities will be reaching 100 degrees or higher, with the added humidity making it really difficult to be outside for a great length of time.

U.S. heat alerts

Heat alerts across the U.S. through Tuesday night (Credit: Fox News)

Some areas across the upper Midwest, the Great Lakes and Ohio Valley will feel some relief as a cold front moves through the region.  

Severe storm threats for the Great Lakes

Storms over the Great Lakes (Credit: Fox News)

That front will bring some thunderstorms and the risk of flash flooding.  

Flash flood threats in the Southwest

The threat of flash flooding in the Southwest. (Credit: Fox News)

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Heavy rain with isolated flash flooding will be possible over the Southwest and Great Basin, as the monsoon season is still in full swing.