Historical perspective on recent heat and cold extremes

Several episodes of societally disruptive extreme heat and cold have occurred in recent years. These include extreme heat in the summers of 2011 and 2012 and extreme cold in the winter of 2013-2014. These particular examples represent persistent conditions of anomalously high or low temperatures. Imbedded in these persistent anomalous conditions are short periods of very extreme temperatures, which I will refer to as cold waves and heat waves. The question addressed in this paper is how these cold and heat waves compare with historical events. I use very simple metrics of extreme heat, defined by duration and recurrence interval. Spatial aggregation of results to the large regional and national scales provides a perspective on both the intensity and spatial extent of recent episodes. When averaged to a national scale, the heat wave number and intensity of the 2011 and 2012 summers was the worst since 1988, but less than the worst years of the 1930s Dust Bowl. The cold wave number and intensity of the 2013-2014 winter is quite notable when a moderate definition of extreme is used, perhaps the worst since the string of cold winters in the late 1970s, but when examining only the most extreme historical cold waves, it was only a little above average. Regional results are being developed and will be presented.