Influence of Synoptic Scale Circulation on Temperature and Equivalent Temperature Extremes in Chicago, IL (1948-2014)

Heat waves are responsible for significant economic impacts and loss of life each year in the United States with humidity often playing an important role. This study examined synoptic patterns associated with extreme temperature and equivalent temperature events in Chicago, IL over the period of 1948-2014 using summertime (June 1st- September 15th) values. Temperature and equivalent temperature-based heat waves were defined as periods with at least eight consecutive six-hour observations exceeding the historical 95th percentile values of temperature and equivalent temperature, respectively, using data from O’Hare International Airport. Self-organizing maps (SOMs) were then applied to 500 mb geopotential height and 850 mb specific humidity datasets from the NCEP/NCAR reanalysis to identify synoptic states associated with extreme temperature and equivalent temperature events. SOM nodes associated with heat waves were identified and assessed for trends using median of pairwise slopes regression. While mean summertime temperature and equivalent temperature in Chicago did not exhibit significant trends, yearly summertime minimum temperatures were found to be increasing with a significant trend. Additionally, several synoptic patterns favorable for the development of high temperature and high humidity heat waves were increasing significantly