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

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.

It was only a matter of time before a long-lived heat wave would develop in the Midwest and Northeast. This one could last from late this week into early next week.