Evolution and maintenance of simulated quasi-stationary mesoscale convective systems

When mesoscale convective systems (MCSs) are organized such that new convection develops upstream of the existing convection and the system as a whole becomes quasi-stationary, the potential often exists for large accumulations of rainfall and flash flooding. This study considers the processes by which MCSs of this type persist for extended periods of time.

The motivation for this work is the flash-flood-producing MCS that occurred on 6-7 May 2000 in eastern Missouri. In this event, a strong low-level jet advected moist air that was lifted to saturation on the downshear side of a mesoscale convective vortex (MCV). As a result, the MCS's inflow was in many areas absolutely unstable to vertical motions. Herein, we initialize idealized simulations with a sounding representative of this inflow environment to examine the nature of the convection that ensues.

In these simulations, a backbuilding MCS develops that is in many ways reminiscent of the 6-7 May 2000 storm. In the simulations, new convection repeatedly develops on the flank of the convective system that is being fed by the LLJ. The results of the simulations suggest that the upstream convection is initiated by a series of processes that are related to both convective downdrafts and gravity waves that are trapped at low levels. These mechanisms allow the MCS to be long-lived without the benefit of strong lifting by a cold pool at the surface.