Jonathan M. Garner<\/em><\/p>\n The significant tornado parameter (STP) has been used by severe-thunderstorm forecasters since 2003 to identify environments favoring development of strong to violent tornadoes.\u00a0 The STP and its individual components of mixed-layer (ML) CAPE, 0-6-km bulk wind difference (BWD), 0-1-km storm-relative helicity (SRH), and ML lifted condensation level (LCL) have been calculated here using archived surface objective analysis data, and then examined during the period 2003-2010 over the central and eastern United States.\u00a0 These components then were compared and contrasted in order to distinguish between environmental characteristics analyzed for three different synoptic-cyclone regimes that produced significantly tornadic supercells: cold fronts, warm fronts, and drylines.\u00a0 Results show that MLCAPE contributes strongly to the dryline significant-tornado environment, while it was less pronounced in cold-frontal significant-tornado regimes.\u00a0 The 0-6-km BWD was found to contribute equally to all three significant tornado regimes, while 0-1-km SRH more strongly contributed to the cold-frontal significant-tornado environment than for the warm-frontal and dryline regimes.<\/p>\nAbstract<\/h4>\n