The term heat dome in reference to extreme heat events has grown in popularity. While a heat dome definition has recently been added to the Glossary of the American Meteorological Society, a quantitative meteorological definition is currently lacking. Here we present such a definition and use it to develop a novel 85-year climatology of extreme heat and associated mid-tropospheric circulation over mid-latitude North America. Our definition groups extreme heat objects (EHOs), defined daily as spatially contiguous regions where 2-meter maximum temperature exceeds the May-September 99 th percentile, into two categories: those directly associated with a 500-hPa closed anticyclone and those that are not. When a closed anticyclone is closely associated with an EHOs on the same day this is labeled a heat dome, with EHOs occurring under these features classified as heat dome EHOs. While heat domes occur across the continent, they are most common south of about 45° north latitude. Overall, 47.1% of EHOs detected are heat dome EHOs. However, when EHOs are considered part of multi-day heat events, 69% are heat dome EHOs. Non-heat dome EHOs occur with a variety of 500-hPa patterns, often, but not always, resembling an open ridge. This illustrates that very extreme heat, relative to climatology, can occur without being part of a heat dome feature and therefore the term should only be used in reference to a specific type of meteorological phenomenon. Results provide insight into the atmospheric drivers of extreme heat with potential to promote more meteorologically precise communication about extreme heat risk.
Loikith et al. (Fri,) studied this question.