Heatwave incoming: How high will temps go and when will it end?

Just in time for summer, here comes the heat.

"A dangerous, widespread heat wave will bake the central and eastern U.S., bringing the hottest temperatures of the year and uncomfortably muggy air to the Midwest and Northeast that in some areas could last into much of next week," Weather.com meteorologist Jonathan Erdman said in an online forecast June 20.

AccuWeather estimates that 170 million people will experience temperatures at or above 90 degrees during the building heat wave into next week.

"The magnitude and longevity of this heat wave will be a shock to the system," AccuWeather senior meteorologist Chad Merrill said.

Heat alerts from the National Weather Service were in place June 20 across large swaths of the central and eastern U.S.