Enormous ‘heat dome’ has caused 22 deaths

Unless you live in the lucky part of the continental United States that will not be slammed by a heat wave this week, you've probably encountered what meteorologists are calling the "heat dome."

A claustrophobia-inducing greenhouse of heat and sadness, the "heat dome" is actually a 1 million square-mile high-pressure system hovering over most of the country and pushing temperatures sky-high. Nearly 150 million Americans in 32 states are in the dome, leading to at least 22 deaths around the country as of yesterday, according to CNN. In Oklahoma alone, state medical officials believe 12 people have died from the heat.

Christopher Vaccaro at the National Oceanographic and Atmospheric Administration (NOAA) tells The Lookout that the United States is facing a unique convergence of heat-stoking forces. The high-pressure system compresses the air--meaning it drives the warm air closer to the ground while heating it up to uncomfortably high temperatures. That compressed, sinking air keeps clouds from forming, giving the sun--which is at its highest angle this time of the year--free rein to do its worst. "Warmer air is thicker than colder air so it's actually a literal dome," Vaccaro explains. The final sweaty blow is that ground winds have consistently been coming from the south, pushing humid tropical air all the way to Northern Midwest states such as Minnesota. The humidity makes the heat even more dangerous, Vaccaro says.

Northern areas usually spared the worst of July heat have been hit hard by this system. Council Bluffs, Iowa, reached 123 degrees on the heat index Wednesday, according to the National Weather Service. The plains areas will get relief today, however, as the dreaded heat dome travels east. You can watch its ominous progress in the NOAA video above.

"Today in Washington, D.C. and Philadelphia, it's going to be the first of three consecutive days at or near 100 degrees. Humidity will make it feel 110 or higher," Vaccaro says.

The "bubble of high pressure" tapers off at its very northern edges, which Vaccaro says creates a "ring of fire" where thunderstorms are cropping up. But the thunderstorms can't penetrate the dome, and are trapped in the north.

While heat waves are not unusual in the summer, this heat wave is lasting a remarkably long time and is very severe. Vaccaro says that larger and longer-lasting heat waves are expected to become more frequent in the future due to the warming climate.

NOAA has released safety tips about how to deal with the heat, which is the number-one weather-related killer in the country.