Is the monthly temperature climate of the United States becoming more extreme?

A new data set of monthly temperatures, adjusted for detected inhomogeneities, was used to examine whether the monthly temperature climate of the U.S. has become more extreme. During the past two to three decades, there has been a shift toward more frequent very warm months, but less frequent very cold months. Thus, overall the monthly temperature climate has not become more extreme. Midtwentieth century including the 1930s was an earlier period of frequent very warm months, a result of very warm daytime temperatures, while nighttime temperatures were not unusual. Regionally, there is a lack of century-scale warming in the southeast U.S. annually and in parts of the central U.S. in the summer, characterized by lack of daytime warming while there has been nighttime warming. Compared to the earlier midcentury warm period, recent decades have been more (less) extreme in the summer (winter) in the west while Midwest summers have been less extreme.