Heat is the number one killer -- and it’s heading to the most densely populated part of America for a prolonged period.

States in the Midwest and Northeast will face high temperatures in the coming days during the summer’s first “dangerous” heat wave, according to the National Weather Service. An expanding heat wave hitting the Southwest and Rockies will shift by the weekend to produce “the most oppressive heat of the season to date” from the Midwest to the Northeast this weekend and next week,

A heat wave forecast to envelop the Midwest and the Northeast with triple-digit weather is expected to arrive on the heels of the first official day of summer. But before the sizzle, the country's midsection and much of the East Coast will have to endure at least a couple of days of severe weather.