Abstract
Long-lived supercells (containing mesocyclones persisting for at least 4 h) are relatively rare, but present significant risk for society as a result of their intensity and associated hazards over an extended time period. The persistence of a rotating updraft is tied to near-storm environmental characteristics; however, given the established prevalence of mesoscale environmental heterogeneity near severe convection, it is unknown to what extent those near-storm characteristics vary over the lifetime of a supercell, nor how quickly the storm responds to such changes. This study examines 147 long-lived, isolated supercells, focusing on the evolution of their near-storm environments using model analysis soundings generated each hour throughout the storm’s lifetime. Environmental variability is quantified via a series of common forecasting parameters, with impacts of measured changes related to production of severe weather and overall storm longevity. The diurnal and maturity-relative distributions of forecasting parameters are examined, along with comparisons among subsets of marginally versus very long-lived supercells, as well as dissipation before versus after sunset. The diurnal cycle is a dominant trend over the lifetime of all supercells, with attendant impacts to relevant thermodynamic and kinematic parameters, timing of storm initiation and dissipation, as well as severe weather production. Notably, changes in the near-storm environment are connected to supercell longevity and generation of severe weather reports. The long-term goal of the above analyses is to enhance short-term forecasts of supercells by better anticipating storm evolution as a result of environmental variations.
Significance Statement
The environments in which severe thunderstorms occur often vary substantially over time and space. To understand how these changes influence the evolution and severe weather production of supercell thunderstorms, the near-storm environments of 147 long-lived supercells were examined using hourly weather model data. Daily patterns of daytime heating and cooling, along with associated changes to the low-level wind profile, dominated the near-storm environmental trends. However, environmental changes appear to be important in distinguishing very long-lived supercells from marginally long-lived supercells, and are also relevant to the production of severe weather. These findings have implications for being able to forecast supercell maintenance and development of tornadoes, large hail, or severe wind gusts.
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