Heat 'dome' traps much of US in pressure cooker

CHICAGO (AP) - For millions of people enduring this week's extreme heat and humidity, it feels like they're living in a pressure cooker. And in a sense, they are.

Much of the United States is trapped under a heat "dome" caused by a huge area of high pressure that's compressing hot, moist air beneath it, leading to miserable temperatures in the mid-90s to low 100s and heat-index levels well above 100 degrees. The oppressive conditions extend from the northern Plains states to Texas and from Nebraska to the Ohio Valley. And they're expanding eastward.