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Circulation patterns (CPs) are discrete categorizations of spatial fields of atmospheric conditions, often used to examine the interaction between the overlying atmosphere and surface weather. Examining changes in the frequency of these atmospheric CPs may therefore help us better understand the relationship between a changing climate and the occurrence of extreme weather events. In this study, we use self‐organized maps to classify CPs from 500 mb geopotential heights (500z) and mean sea‐level pressure (MSLP) for five regions across North America, using two different reanalysis datasets. Trends in CPs (from 1979 to 2018) from both the North American Regional Reanalysis (NARR) and the recently released ERA5 datasets are compared using a new method in which the CPs from the ERA5 dataset are based on the principal components of the NARR data. This results in a more direct comparison between the CPs of each dataset. z500 CP trends were generally larger than the MSLP CP trends and the NARR CP trends were generally larger than the ERA5 CP trends. Furthermore, the most extreme summer‐dominant CPs were found to have increased significantly over the 40‐year study period in all five regions for both the NARR and ERA5 CPs. [ABSTRACT FROM AUTHOR]

Concurrent with the background rise in global mean temperatures, changes in extreme events are also becoming evident, and are arguably more impactful on society. This research examines trends in three components of seasonally‐relative extreme temperature and humidity events in North America that directly influence human thermal comfort: event frequency, duration, and areal extent. Results indicate that for the majority of the study domain, changes in these events are in the expected direction with changes in means. Extreme heat events are generally increasing throughout the domain, with the largest changes in summer and autumn in the eastern portion of Canada and the United States. Cold events are largely decreasing in these same locations and seasons, with additional widespread decreases in winter. Interestingly, significant increases in cold events are also evident in autumn in parts of the western United States. Extreme humidity events are showing an even greater change than temperature events – nearly all of Canada and most of the United States is seeing significant increases in extreme humid events and decreases in dry events, while the southwestern deserts show widespread significant increases in dry events, especially in winter and spring. Changes in event duration and spatial extent mimic these results. Importantly, this research demonstrates that there are regions that show changes to extreme events that differ from the overall changes in means, highlighting the importance of looking beyond climate averages to examine not only extreme events, but changes in higher‐order statistical moments. [ABSTRACT FROM AUTHOR]