Spatial associations between tornado activity and meteorological variables in the contiguous United States

Abstract

There is evidence of a decrease in contiguous US tornado activity in the Great Plains, and an increase in the Southeast over recent decades. Little research has addressed how environmental factors contribute. This thesis assessed how three “ingredients” of tornado activity, specific humidity (moisture), storm relative helicity (wind shear), and convective available potential energy (instability) have changed. This assessment consisted of a regional time series analysis and a comparison of spatial changes in tornado activity with those of these environmental variables across three periods. This study confirms changes in tornado activity and reveals that tornado ingredients have increased in the Southeast and lower Midwest during winter. This study also reveals increases in storm relative helicity in the Great Plains during winter and spring despite the decrease in tornado activity. Lastly, these tornado ingredients did not change significantly in the Southeast and lower Midwest despite the corresponding increase in tornado activity.