Thermodynamic sensitivities in observed and simulated extreme-rain-producing mesoscale convective systems

Wednesday, 16 December 2015: 16:45
3006 (Moscone West)
Russ S Schumacher, Colorado State University, Fort Collins, CO, United States and John M. Peters, Colorado State University, Department of Atmospheric Science, Fort Collins, CO, United States
Mesoscale convective systems (MCSs) are responsible for a large fraction of warm-season extreme rainfall events over the continent
al United States, as well as other midlatitude regions globally. The rainfall production in these MCSs is determined by numerous
factors, including the large-scale forcing for ascent, the organization of the convection, cloud microphysical processes, and the
surrounding thermodynamic and kinematic environment. Furthermore, heavy-rain-producing MCSs are most common at night, which means
 that well-studied mechanisms for MCS maintenance and organization such as cold pools (gravity currents) are not always at work. 
 In this study, we use numerical model simulations and recent field observations to investigate the sensitivity of low-level MCS s
tructures, and their influences on rainfall, to the details of the thermodynamic environment. In particular, small alterations to
 the initial conditions in idealized and semi-idealized simulations result in comparatively large precipitation changes, both in t
erms of the intensity and the spatial distribution. The uncertainties in the thermodynamic enviroments in the model simulations w
ill be compared with high-resolution observations from the Plains Elevated Convection At Night (PECAN) field experiment in 2015. 
The results have implications for the paradigms of "surface-based" versus "elevated" convection, as well as for the predictability
 of warm-season convective rainfall.