Synoptic Characteristics of Extreme Heat Days in the Southeastern United States

Heat events have the ability to cause large-scale loss of life, and climate models predict an increase in summer temperatures in the southeastern United States in the coming decades.  Therefore, it is important to understand the circulation characteristics of extreme heat days so that future heat events can be better predicted.  This study examines the characteristics of extreme heat days in July-August in the southeastern United States over a 37-yr period (1979-2015).  Mean daily temperature and dew-point temperature data were acquired for 63 weather stations, and the stations were combined into eight heat regions.  Days in the top 5% based on mean daily apparent temperature were classified as extreme heat days.  The far northwestern and northeastern sections of the Southeast had the largest deviations in apparent temperature between extreme heat days and mean seasonal apparent temperature, while southern Florida had the smallest deviations.  Extreme heat days in all regions except southwestern Florida were clearly associated with migratory anticyclones situated to the west of the regions, with the two northern regions having the largest positive anomalies in geopotential heights.  Therefore, a westward expansion of the Bermuda High is not a direct cause of extreme heat days.  All regions had a disproportionately large number of trajectories entering the region from the west on extreme heat days.