“Heat dome” is a term used explain extreme heat conditions across large geographic regions.

The American Meteorological Society maintains a glossary of meteorological terms and defines a heat dome as, “An exceptionally warm air mass at middle latitudes during the warm season that that is associated with a synoptic-scale area of high pressure aloft. This area of high pressure aloft can have a doming effect on the warm air mass below by suppressing rising motion and the development of clouds and precipitation.” This is not the same as a heat wave, which is a spell of 3 or more abnormally hot days.
A heat dome develops when a ridge of high pressure builds over an area and resides there for a week or more. High pressure is associated with very few clouds and lots of sunshine, leading to warm temperatures near the surface. The sinking motion in the high pressure prevents warm air near the surface from rising. This subsidence motion causes further warming of the air by compression. Unless the upper atmospheric pattern changes, the high pressure will continue to exacerbate the hot conditions. The ground also warms and loses moisture, which can lead to drought conditions and the risk of wildfires. The term “ring of fire” is a weather term that is a related to heat dome, as it describes thunderstorms that develop at the boundaries of the heat dome.
Hot and humid conditions during a heat dome can lead to heat-health issues. When our bodies get hot, we cool down by sweating. The sweating does not directly cool our bodies; it is the evaporation of the sweat that cools us. If the air has a high humidity, then the rate of evaporation is reduced, hampering the body’s ability to maintain a constant internal body temperature.
Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at noon the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.