An intense and nearly historic weather pattern is cooking much of America under a dangerous heat dome this week with triple-digit temperatures in places that haven't been so hot in more than a decade.

Let’s start with what “normal” or “average” is for July, August and September. July and August average high temperatures are between 80 degrees north and 83 degrees south. September’s temperatures typically start to cool a touch into the 70s by the end of September.