Evaluating the Effective Inflow Layer and Supercell Updraft Intensity in a Variety of Realistic Environments

Accurately assessing the layer of the atmosphere from which thunderstorms draw their inflow is critical to determining the processes that will control updraft intensity. Predicting the effective inflow layer (EIL) for supercell thunderstorms is especially critical given the potential for both dynamic and buoyant updraft accelerations. Important environmental parameters like CAPE and storm-relative helicity are dependent on averaging or integrating over the best estimate of the effective inflow layer, and these are critical for predicting and understanding supercell mesocyclone properties including updraft intensity and rotation. The current widely used EIL formula depends only on parcel buoyant potential energy, thus it remains unclear how accurate it is in representing the true inflow layer for supercells, where dynamic updraft forcing is as or even more important than buoyancy.

In order to determine how the true inflow layer for supercell updrafts varies over a range of thermodynamic and kinematic environments, results from a series of idealized simulations of supercell and nonsupercell thunderstorms will be presented. Several Rapid Refresh model analysis proximity soundings from distinct regimes of real events that result in significantly tornadic, weakly tornadic, nontornadic supercells and nonsupercell thunderstorms are used to initialize idealized numerical simulations. Thermodynamic soundings are modified in sensitivity tests to add surface stable layers of varying intensity to modify the base-state EIL. Analysis of passive tracer concentrations and updraft back trajectory origin heights and locations are used to determine how the inflow layer varies in each regime. Results indicate that despite significant changes in buoyancy versus nonhydrostatic dynamic and buoyancy pressure perturbation updraft forcing mechanisms between simulations, buoyancy remains the best predictor of peak updraft strength. The current formulation of the EIL performs well for supercell storm types, but not for nonsupercell storm types, with significant entrainment of air above the EIL into nonsupercell updraft cores. While the EIL metric encompasses most air that enters supercell updraft cores, large portions of the EIL are often unused by the updraft core. Thus a metric for inflow more narrowly focused on the most unstable parcel layer may be more reflective of the true inflow layer.