Subtropical/polar jet influence on Plains and Southeast tornado outbreaks

Abstract

While extensive research consideration has been given to the Northern Hemispheric polar (PJ) and subtropical jet (STJ) streams, there have been fewer climatological studies relating these two jet types to tornado outbreaks. This study examines tornado outbreaks in two regions with substantial tornado risk, Plains Tornado Alley (PTA) and Southeast Tornado Alley (STA), and classifies the jet streak types associated with the outbreaks. Utilizing the Storm Prediction Center (SPC) tornado database and an objective jet identification scheme created from NCEP/NCAR Reanalysis 1 data, jet streaks were identified as STJ, PJ, merged (identified as STJ and PJ), superposed, or unidentified for a 30-year period between 1984 and 2013. Tornado outbreaks were categorized into different types based on these jet streak types. Results revealed STJ and PJ tornado outbreaks compose the majority of tornado outbreaks, as well as the most intense outbreaks, in both PTA and STA. STJ tornado outbreaks were found to be more common in PTA than in STA, while PJ outbreaks were more common in STA than in PTA. The study concludes by considering how a coupled jet structure may be important for tornado outbreaks.