Radar Climatology of Precipitation Features in Close Proximity to Supercell Tornadic Storms

This study is concerned with a new research thrust examining the impact of evaporational cooling by rain on boundary layer thermodynamic and wind profiles within or near the inflow region of supercell storms. In order to determine the relative frequency of this process, we are developing a radar climatology to document the relative frequency of various precipitation features that form within, or translate into, the supercell inflow region. Although several published case studies have examined relationships between cell/storm mergers and tornadoes, this work is following a more systematic approach, which is generally focused on changes within the boundary layer. This investigation is documenting the relative frequency of occurrence of precipitation features for supercell storms that produce significant tornadoes for various geographic regions (Southeast, Midwest, Great Plains), but with an initial focus on supercell tornadic storms within the Southeast region. This radar climatology includes the following components:

1. Fraction of storms that come into close proximity to precipitation within or near the relative low-level storm inflow sector;
2. The persistence of precipitation within the inflow sector, and the relative timing between arrival of precipitation (for transient or propagating precipitation features) and tornadogenesis;
3. Classification of the precipitation features into the categories stratiform, shallow convective showers (isolated or in clusters), deep convective showers (isolated or in clusters), and curvilinear bands;
4. Characteristics of kinematic vigor and precipitation based on radial velocity and polarimetric measurements (e.g., Zh, ZDR, Kdp).

The working hypothesis is that precipitation features near or within supercell inflow regions are more common around Southeast supercell storms due to lower values of CIN and a greater propensity for relatively shallow convection to produce rain via the warm rain process. This study is closely related to the rapid transition in boundary layer stability, and associated increase in low level winds above the surface layer, that are hypothesized to increase low-level storm-relative helicity (0 to 0.5 km, or 0 to 1 km), while simultaneously decreasing the LCL.