A heat wave is moving in, with over 100 million people from the Midwest to the Northeast on alert for life-threatening heat this weekend and into next week.

Maps show where extreme humidity and 90- or 100-degree temperatures will affect around 255 million people across the United States.

A few locations could approach or top 100 degrees, including Denver, which happens only twice a year on average, said Weather.com meteorologist Jonathan Erdman, who added that "New York City and Philadelphia could also flirt with the century mark during the peak of the heat wave next week.