A heat dome is a mass of abnormally warm air that extends from the surface to well into the atmosphere. It is associated with high pressure both at the surface and aloft. Heat domes develop when the atmosphere traps hot air, as if bounded by a lid or cap. The upper air weather patterns are slow to move, referred to by meteorologists as an Omega block.
Creation of heat domes
In still, dry summer conditions, a mass of warm air builds up. Sinking air with the high pressure pushes the warm air down. The air is compressed, and as its net heat is now in a smaller volume, so it must get hotter. As the ever warmer near the surface air attempts to rise, the high pressure above it forces it down, to get hotter, and its pressure grows higher.
The high pressure acts as a dome, or lid, causing everything below it to get hotter and hotter. The upper-level high pressure blocks any rain-making systems. The sinking air suppresses cloud formation, thus allowing intense summer sunlight to heat the air near the ground. In summer, heat domes are associated with heat waves at the surface and can last for weeks.
500mb pressure chart showing Heat dome over southern British Columbia June 2021. Base chart image source NOAA [wikicommons].
Weather blocks can persist for days weeks or even months until the pressure pattern changes.
Simple animation of the heating process within a heat dome [by kind permission of the Royal Metoerological Society]
Impact of Heat dome on flight operations
Temperate zone infrastructure is often not designed for the high temperatures associated with a heat dome. As a consequence, there may be challenges associated with interruptions to power supplies, damage to operating surfaces at airports, or systems failures which may cause delays and capacity problems that affect multiple airports and service providers.
Furthermore, the prolonged hot and dry weather can increase the risk of wildfires and heat-health issues.
Flights through the heat dome will experience higher than usual (ISA) outside air temperatures at medium and higher flight levels with a consequent impact on aircraft performance, e.g. fuel consumption.