Objective Climatological Analysis of Warm Season Extreme Events during the North American Monsoon

Almost half of the annual precipitation in the Southwest U.S. is caused by convection related to the North American Monsoon (NAM), which occurs during a three month time-span in the summer. The NAM can produce severe thunderstorms that coincide with high winds, dust storms, lightning, hail, and flash floods and can have major societal impacts on semi-arid regions. Our research uses objective analysis in both reanalysis and observational data to determine the dominant synoptic patterns and wind profiles associated with NAM extreme events in the late 20th century. The statistical analysis was designed to categorize the dominant synoptic patterns of extreme events and modes of variability. Historical extreme events are selected based on convective available potential energy (CAPE) values exceeding the 90th percentile, while taking into account the diurnal cycle of convection during the NAM. The synoptic condition of the identified extreme events are further analyzed using eigenvector orthogonal function/principle component analysis (EOF/PC), which has the ability to connect the NAM extreme event classification to the dominant patterns of the synoptic-scale circulation. Using both the 500mb geopotential height field for the EOF analysis and the wind components of the wind profile for an extended EOF creates a three dimensional relation of the specifications of the synoptic patterns associated with the convective storms. The overall approach to the objective analysis will provide a climatological methodology in extreme convective event projection in the NAM region and other semi-arid regions.