Entraining CAPE for Better Assessment of Tornado Outbreak Potential in the Warm Sector of Extratropical Cyclones

Abstract

AbstractConvective available potential energy (CAPE) is known to lack skill in discussing the environments of tornadic and nontornadic storms, or those of tornado outbreaks and nonoutbreaks. In this paper, a composite analysis of extratropical cyclones that caused 15 or more tornadoes [outbreak cyclones (OCs)] and 5 or fewer tornadoes [nonoutbreak cyclones (NOCs)] in the United States in April and May between 1995 and 2012 shows that entraining-CAPE (E-CAPE), which considers the effects of the entrainment of environmental air, is useful in the analysis of the environments of OCs and NOCs. E-CAPE in the warm sector of OCs is larger than that in the warm sector of NOCs (statistically significant at the 95%?99% level). Moreover, the regions with large E-CAPE for both OCs and NOCs are more closely correlated with the locations of tornadoes than those with large CAPE. The larger E-CAPE near the center in the warm sector of OCs is due to greater moisture at low and midlevels that results from advection by strong southerly winds and synoptic-scale ascent, respectively. The composite analysis also shows that E-EHI, E-SCP, and E-STP, for which traditional CAPE used in the energy helicity index (EHI), supercell composite parameter (SCP), and significant tornado parameter (STP) is substituted by E-CAPE, are more strongly correlated with tornado locations than are the original EHI, SCP, and STP, respectively.