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A favorite piece of jargon for TV meteorologists and weathermen during this scorching week has been "heat dome": some sort of high pressure shroud of blazing hot weather keeping the Midwest, East Coast and large swaths of the West in the high 90s and lower 100s. So for us non-weather experts, what is a heat dome?

Eli Jacks, a meteorologist at the National Weather Service tells the Associated Press a heat dome is a kind of perfect storm of sizzling summer weather exacerbated by relatively cloudless skies and the higher angle of the sun in the summer. "When a high pressure system develops in the upper atmosphere, the air below it sinks and compresses because there's more weight on top, causing temperatures in the lower atmosphere to heat up," he tells the news agency. "The dome of high pressure also pushes the jet stream and its drier, cooler air, farther north — it's now well into Canada — while hot, humid air from the Gulf of Mexico circulates clockwise around the dome, traveling farther inland than normal."

So what parts of the country are being hit with the heat dome? While all the lower 48 states are facing a one-of-a-kind heat wave breaking 221 records across the country, the specific high pressure dome began in the upper Midwest, the National Weather Service tells NPR. The humidity and sky high temperatures made for incredible heat indexes including measurements of 129 degrees in Newton, Iowa, 122 in Gwinner, North Dakota and 121 in Taylorville, Illinois. On Thursday, the heat dome began moving east covering a slew of cities including Philadelphia, New York and Washington, D.C. The AP's Tom McElroy describes the bleak forecasts for today. "The high temperatures and smothering humidity will force up the heat indexes," he writes. "Boston's 99 degrees on Friday could feel like 105 degrees; Philadelphia's 102 degrees like 114 degrees and Washington, D.C.'s 103 degrees could seem like 116."