Heat Wave Will Continue Into August

A stubborn high-pressure system is the culprit behind the dangerously high heat wave that's been baking much of the U.S., experts say. The high-pressure system—a large area of dense air—is being held in place by upper-level winds known as the jet stream. Within the system, dense air sinks and becomes warmer, and since warm air can hold more moisture than cooler air, there's also very high humidity.

Stationary high-pressure systems aren't unusual during the summer, according to Eli Jacks, a meteorologist at the National Weather Service headquarters in Silver Spring, Maryland. But what sets this system apart is its size and strength. "It's exceptionally strong and very wide, covering thousands of miles from border to border and from the Rocky Mountains to the East Coast," Jacks said.

Experts differ about whether global warming is influencing the extended period of very high heat, but Kerry Emanuel, a meteorologist at the Massachusetts Institute of Technology, said the current extreme heat is "happening in the context of climate warming in general. Events like this will become more frequent."

In addition to the heat, the high humidity can be dangerous to human health, noted Maryland-based meteorologist Jacks. During periods of unusually high humidity, sweat doesn't act as a natural cooling agent, Jacks said. "The body can't evaporate moisture—it can't cool itself off," he said. "The body temperature actually starts rising." The heat has already been blamed for about two dozen deaths across the U.S. this week. Unfortunately, sweltering temperatures are predicted to continue their grip on the Midwest, the Northeast, and the South.

Jacks, the Maryland-based meteorologist, added that the above-average temperatures would continue in much of the nation into August. Oh, please, no more. The only cool place is the mall.