Heat-index values are likely to top 110 degrees this week in parts of the country.

When your various sweat streams merge this week, creating a miniature Niagara Falls flowing directly into your pants, blame something called a “heat dome.”

The meteorological phenomenon, which will build through Friday, is expected to roast the Midwest, the northern/central Plains, and beyond with 100-plus degree temperatures. Taking the heat index into account, it might feel as hot as 110 or above. “Nighttime conditions will remain warm and muggy,” says the National Weather Service, “providing little chance for relief.” The worst of the roasting is likely to fall on Thursday and Friday, adds the service, which is cautioning people against going outside during the afternoon. (And seriously, think twice about hiking—that’s what killed several people during last month’s heat wave in Arizona.)

The scalp-sizzling weather is coming from summer warmth and a big ol’ blob of high pressure, combining into that aforementioned dome. The folks at NOAA explain:

A heat dome occurs when high pressure in the upper atmosphere acts as a lid, preventing hot air from escaping. The air is forced to sink back to the surface, warming even further on the way. This phenomenon will result in dangerously hot temperatures that will envelop the nation throughout the week…. In response, the National Weather Service has issued heat alerts for more than a dozen states across the U.S.

Cold-loving people who fear withering like a raisin should head to either Seattle or San Francisco, to judge from these expected highs from NOAA’s Weather Prediction Center. Here’s Thursday:

NOAA/WPC

And Friday:

NOAA/WPC

Correction: This story originally used a graphic provided by NOAA of predicted high temperatures. A NOAA spokesman says the agency has “since learned the image and caption do not match,” so we have removed the graphic, which is still available here.

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