Source air feeding convection within a nocturnal mesoscale convective system during the evolution from surface-based to elevated convection

Although nocturnal convection is frequently observed, the mechanisms that allow nocturnal mesoscale convective systems (MCSs) to persist are still not well understood. On 9 August 2014 at approximately 2000 UTC, a regime of upslope flow owing to a weak shortwave impulse in the lee of the Rocky Mountains spawned a convective complex near the Colorado-Kansas border. Following storm initiation, the system grew upscale into a southeastward-propagating MCS, which became elevated as it continued into the overnight hours, producing severe surface winds and severe hail. This study investigates the elevation above ground level (AGL) from which air parcels with the greatest convective available potential energy (CAPE) originate and support the development and maintenance of elevated convection. The analysis of this system uses WSR-88D composite reflectivity data, a short term forecast from the Weather Research and Forecasting (WRF) model, and back trajectories produced by the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. This paper describes the evolution of the boundary layer as well as the spatial and temporal progression of the altitude of the most unstable (MU) CAPE of air parcels associated with the elevated convection and the connection the source air had with the highest reflectivity produced in the MCS. The change in the source of these parcels over time shows that this particular MCS became elevated and sustained itself off parcels with MU CAPE residing between 1.0 and 1.5 km. It was found that these parcels originated in a different air mass than the parcels with MU CAPE feeding the storm from the surface earlier in the system’s evolution