Environmental Evolution of Long-Lived Supercells

Long-lived supercells (lasting at least 4 hours) are relatively rare, but present significant risk for society as a result of their intensity and associated hazards over an extended time period. As has been shown in many previous studies, the persistence of a rotating updraft is tied to near-storm environmental characteristics such as deep layer vertical wind shear and storm-relative helicity. However, given the prevalence of mesoscale environmental heterogeneity near convection, it is unknown to what extent such near-storm characteristics change over the lifetime of the supercell, and how quickly the storm responds to such changes. For example, how do environmental variations specifically influence fluctuations in storm intensity or production of severe weather, or the exact lifetime of the supercell? To answer such questions, an analysis was conducted of a large number of observed supercells that remained relatively isolated over their extended lifetimes. General characteristics such as storm lifetime, supercell lifetime, and geographic locations were identified, along with associated reports of large hail, strong winds, or tornadoes. The near-storm environment of each supercell was collected each hour throughout its lifetime using model soundings, and quantified using numerous common forecasting parameters. The hourly distribution of each sounding parameter will be shown and correlated with trends in production of severe weather, as well as overall storm longevity. The overall goal of this study is to enhance short-term forecasts of supercells by better anticipating storm evolution, intensity, and duration as a result of environmental variations.