A climatology of heat domes over North America

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.