What is a heat dome?

Something called a "heat dome" is contributing to the scorching heat we've seen in the Midwest and other central states this week.

(FOX 9) - Something called a "heat dome" is driving the scorching heat we've seen in the Midwest and other central states this week.

What is a heat dome?

It's a term that really we don't deal with that often in our portion of the Midwest. The Twin Cities is a zone that's in between two extremes: the cooler, drier air to the north in Canada and the hot, humid air in the southern states.

Something like a heat dome will come and the northern edge can cover the metro and parts of Minnesota. But it's not a long-lasting feature.

Looking at a weather map, it's easier to see right now. From the Cities all the way to the Gulf of Mexico, from Wichita and Dallas, all the way east to Cincinnati, stretching all the way down to parts of Mississippi, a hot, humid air mass dominates the forecast. Excessive heat warnings are in place across that block of the central United States.

It breaks down to a central area of high pressure and circulating air contained in the air mass. It ends up doing two things: It keeps us very hot and humid, but also very dry. Moisture will be diverted on either side, north, south, east and west in something we call the "ring of rain" rotating around this very dominant area of high pressure.

Why is it a dome?

The dome effect comes as the heat expands and the hot air mass expands upward from the (deleted word) surface, pushing up into the atmosphere. With the motion around that high-pressure zone in the dominant air mass, the high sits right on top.

You end up -- and I hate to use this as an analogy -- but most folks realize that a convection oven is all about moving the air around to make it hotter. This is exactly what the heat dome is doing for us. The heat domes don't last too long, but when they're in place, we tend to break record-high temperatures and go well into the triple digits with heat indices.