Abstract
The average temporal and spatial distributions of thunder events (periods of discrete thunder activity heard at a point) in the conterminous United States were found to be generally similar to those of thunder days. Annual averages of thunder events peak along the Gulf Coast (>100) and are also quite high in the central United States (Kansas, Missouri, Illinois with >75 events), and in the southwest (Arizona with 60 events). Thunder events are least along the west coast (<20) and in the northeast (<30). Multiple events per day are greatest in the Midwest (Illinois, Iowa) averaging 1.7 events per summer day, and are also high in the southwest (Arizona) with 1.5 events. This causes these two maxima in thunder event activity to be more pronounced than those found on the pattern of average thunder days.
The average patterns for the thunder event frequencies, multiple events per day, and durations reveal that convective activity is weakest and shortlived along the west coast and in the northeast. The high incidence of events per day in the Midwest reflects multiple storm incidences likely related to MCCs and nocturnal storm activity. The peak in thunder event activity is present in the central United States in all months and rotates from the lower Mississippi Valley to the central Great Plains-Midwest and then back, and its position is always closely related to the major center of cold frontal activity. The thunder peak in the southwest is related to the summer monsoon intrusion of moist tropical Pacific air and related frontal activity. The summer-fall peak in thunder events along the Gulf Coast-Florida is a result of sea breeze induced convergence, localized heating, and occasional tropical disturbances.
