A Recent Climatological Look at Tornado Events Relative to Sunset

Climatologically, tornadoes are most frequently observed in the afternoon and early evening hours during spring and summer in association with convection forced by solar heating. With sunset typically comes the disappearance of solar heating, the collapse and stabilization of the boundary layer, and the demise of tornadoes. However, occasionally this does not occur- tornadoes are observed before sunset and continue after sunset into the night. Even more infrequently, tornadoes are not observed before sunset, but first occur after sunset. Troublingly, such only nocturnal cases present an elevated threat scenario and difficult forecasting challenge. This research first assesses a 15-year climatology of each of these scenarios over the contiguous United States (CONUS) to determine where, when, and how often each of these tornado scenarios occur. Environmental characteristics are analyzed through a combination of composite analysis, standardized anomaly analysis, clustering, and objective classification to assess and contrast meteorological conditions and storm types associated with each of these event classes.