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ABSTRACT
A sample of 1185 Rapid Update Cycle (RUC) model analysis (0 h) proximity soundings, within 40 km and 30 min of radar-identified discrete storms, was categorized by several storm types: significantly tornadic supercells (F2 or greater damage), weakly tornadic supercells (F0-F1 damage), nontornadic supercells, elevated right-moving supercells, storms with marginal supercell characteristics, and nonsupercells. These proximity soundings served as the basis for calculations of storm-relative helicity and bulk shear intended to apply across a broad spectrum of thunderstorm types. An effective storm inflow layer was defined in terms of minimum constraints on lifted parcel CAPE and convective inhibition (CIN). Sixteen CAPE and CIN constraint combinations were examined, and the smallest CAPE (25 and 100 J kg^sup -1^) and largest CIN (-250 J kg^sup -1^) constraints provided the greatest probability of detecting an effective inflow layer within an 835-supercell subset of the proximity soundings. Effective storm-relative helicity (ESRH) calculations were based on the upper and lower bounds of the effective inflow layer. By confining the SRH calculation to the effective inflow layer, ESRH values can be compared consistently across a wide range of storm environments, including storms rooted above the ground. Similarly, the effective bulk shear (EBS) was defined in terms of the vertical shear through a percentage of the "storm depth," as defined by the vertical distance from the effective inflow base to the equilibrium level associated with the most unstable parcel (maximum θ^sub e^ value) in the lowest 300 hPa. ESRH and EBS discriminate strongly between various storm types, and between supercells and nonsupercells, respectively.
1. Introduction
Supercell thunderstorm environments, from both observations and numerical simulations, typically consist of relatively large buoyancy and vertical shear through a substantial depth of the troposphere. Numerical simulations (e.g., Weisman and Klemp 1982, 1984, 1986; Weisman and Rotunno 2000) have established that strong vertical wind shear, generally greater than 20-25 m s^sup -1^ wind variation over the lowest 4-6 km above ground level (AGL), is necessary for the maintenance of long-lived supercell structures. Sufficient vertical shear through this depth allows for the establishment of the characteristic mesocyclone structure in right-moving supercells, such that precipitation and associated evaporative cooling do not disrupt low-level storm inflow (Weisman and Rotunno 2000; Rotunno and Weisman 2003). Though some disagreement exists...