A series of low pressure systems are moving across the Northern Tier, bringing welcomed cooler air behind it, while the South stays sweltering. These cooler temperatures will be a nice taste of fall for the North as temperatures are forecast to be in the 60s and 70s, which is 5 to 15 degrees below average. Meanwhile, the relentless summer heat in the South has no plans of leaving, with brutal triple-digit heat indices. Here are all the details.