Heat dome
A heat dome is a persistent high-pressure pattern that traps and intensifies hot air near the surface, often producing dangerous multi-day heat waves.
What a heat dome is
A heat dome is a persistent area of high pressure that helps trap hot air over a region. The term describes the way sinking air can act like a lid, suppressing clouds and storms while allowing heat to build at the surface. Heat domes often last for several days and can sometimes persist for weeks.
How high pressure traps heat
Under high pressure aloft, air sinks toward the surface. As it descends, it compresses and warms. The sinking motion also discourages rising air, cloud formation, and thunderstorms that might otherwise bring shade or rain. Clear skies then allow strong sunlight to keep heating the ground and lower atmosphere.
Blocking and the jet stream
Heat domes often form within slow-moving upper-air patterns. A northward bend in the jet stream can create a ridge, and a blocking pattern can keep that ridge in place. When weather systems are forced around the block, the same region may stay hot and dry day after day.
Heat dome versus heat wave
A heat wave is a period of unusually hot weather. A heat dome is one atmospheric setup that can cause or intensify a heat wave. Not every heat wave is a textbook heat dome, and not every high-pressure ridge produces extreme heat. The local outcome depends on season, soil moisture, humidity, elevation, wind, clouds, and the region's normal climate.
Humidity and nighttime heat
Humidity can make a heat dome more dangerous by raising the heat index and limiting the body's ability to cool through sweat evaporation. Warm nights are also important. If buildings, pavement, and bodies do not cool down overnight, heat stress can accumulate over multiple days.
Urban and wildfire impacts
Cities can become especially hot under a heat dome because pavement, roofs, traffic, and limited tree cover store and release heat. Dry heat domes can also worsen drought, dry vegetation, and wildfire risk. Power demand often rises as people use air conditioning, which can strain electrical grids during the highest-risk hours.
Climate change context
Heat domes are not new, but a warmer climate raises the baseline temperature on which weather patterns operate. That means similar pressure patterns can produce hotter extremes than they would have in a cooler climate. Researchers also study whether warming may affect the persistence of blocking patterns in some regions.
Why it matters
Heat domes turn atmospheric circulation into a public-health, infrastructure, agriculture, and ecosystem problem. Understanding them helps explain why heat risk can build slowly, why alerts may focus on both daytime highs and overnight lows, and why cooling centers, shade, hydration, and neighborhood design matter during extreme heat.