Observations of Wall Cloud Formation in Supercell Thunderstorms during VORTEX2

Abstract

Abstract This study presents an integrated analysis of dual-Doppler, cloud photogrammetry, surface mobile mesonet, and sounding data to examine wall cloud formation in two supercells observed during the Verification of the Origins of Rotation in Tornadoes Experiment II (VORTEX2). One of the wall clouds contained significant rotation and spawned an (enhanced Fujita) EF2 tornado, while the other was clearly displaced horizontally from the mesocyclone and exhibited little rotation at the time of data collection. Backward parcel trajectories show that the majority of the air entering the wall cloud base originates in the forward-flank region. A small fraction of the parcels enter the wall cloud base from the inflow. Some rear-flank downdraft parcels descend into the strongly rotating wall cloud. For both wall clouds, much of the observed wall cloud lowering is attributed to evaporatively cooled parcels in the forward-flank region being ingested into the low-level updraft. Additional wall cloud-base lowering is observed near the circulation center of the strongly rotating wall cloud. This localized lowering is created by the pressure deficit and associated cooling. The observational results presented herein are compared to long-standing wall cloud formation conceptual models published in the refereed literature.