(CNN) A dangerous and potentially deadly heatwave threatens much of the continental US, with dozens of record high temperatures both in the daytime and in the evening expected this weekend.

More than 150 million people in nearly 30 states were under a heat watch, warning or advisory on Thursday morning, according to CNN meteorologist Dave Hennen.

Over the next few days, more than 85 percent of the lower 48's population will see temperatures above 90 degrees Fahrenheit, Hennen said, and more than half will see temperatures in excess of 95 degrees.

Much of the heat expected for Thursday was forecast to descend on the Midwest and Mississippi, before making its way to the Northeast on Friday and Saturday, Hennen said.

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