Zoe Schroder Searcy 

Global climate features are known to influence tornado frequency in the U.S., but more work needs to focus on understanding the extent to which climate variables contribute to increases in CAPE and shear on days with an outbreak of at least ten tornadoes. Here the authors quantify the conditional relationships between precursor SST and SLP variables and localized extremes of CAPE and shear associated with large outbreaks. They do this by fitting linear regressions to global climate variables averaged over the fifteen days before the outbreak to estimate the changes in CAPE and shear on days with at least ten tornadoes. Results show that for every 1° increase in the SST gradient between the Gulf of Alaska and the Caribbean, DLBS increases by 0.88 m s¯¹, SLBS increases by 0.62 m s¯¹, and CAPE decreases by 50.6 J kg¯¹, conditional on at least ten tornadoes, and holding the other variables constant. Further, results show that for every 1° E increase in longitude, DLBS increases by 0.15 m s¯¹, SLBS increases by 0.38 m s¯¹, and CAPE decreases by 39.3 J kg¯¹, conditional on at least ten tornadoes, and holding the other variables constant. Additionally, SLBS is the only environmental factor that has a significant upward annual trend.