Heat dome

A heat dome is a weather phenomenon consisting of extreme heat that is caused when the atmosphere traps hot ocean air, as if bounded by a lid or cap. Heat domes happen when strong high pressure atmospheric conditions remain stationary for an unusual amount of time, preventing convection and precipitation and keeping hot air "trapped" within a region. This can be caused by multiple factors, including sea surface temperature anomalies and the influence of a La Niña. The upper air weather patterns are slow to move, referred to by meteorologists as an Omega block.

The term is often extrapolated in media terminology for any heat wave situation, though heat waves differ as they are periods of excessively hot weather not necessarily caused by such stationary high-pressure systems. The term heat dome is also used in the context of urban heat islands.