Properties of Elevated Convection in the Comma-head of Continental Winter Cyclones

Understanding processes in the comma-head of winter cyclones is important due to the high impact weather in this region. Improved knowledge will allow better interpretation of observations and improved simulation of cold season extratropical cyclones. In this work, we examine the properties of the elevated convective cells found on the equatorward side of the comma head region of these cyclones. This study utilizes radar data from the Wyoming Cloud Radar (WCR) taken during the Profiling of Winter Storms (PLOWS) field campaign. Radar observations from multiple cases within different types of cyclones show that these convective cells are common features in the comma head region, with cells in the more intense cyclones occasionally producing lightning discharges. The convective cells examined are shown to have updrafts exceeding 5 m s^-1 using contoured frequency by altitude diagram (CFAD) analysis and are sourced above an elevated front in the comma head and extend several kilometers in the vertical, often to the tropopause. The radar observations are supplemented with results of 3 km resolution, cyclone-scale Weather Research and Forecasting (WRF) model simulations in order to show the magnitude of the elevated potential instability within the comma head responsible for these convective cells. Additionally, trajectory analysis is used to illustrate the development of instability in the comma head as a dry airstream overlies a moist airstream, leading to the generation of positive CAPE with respect to ice.