Studies of Midlatitude Mesoscale Convective Systems

Colorado State University, Fort Collins CO

Investigators

Abstract

The objective of this research is to enhance understanding of processes associated with midlatitude mesoscale convective systems (MCSs) and their accompanying severe weather, and ultimately to improve the prediction of such systems. Of particular interest are MCSs having varying patterns of organization of their attendant stratiform precipitation regions and those producing high winds and extreme rainfall. At present, the surface meteorological features associated such systems are not well documented. To address this problem, the Principal Investigator will utilize surface observations from the Oklahoma Mesonet (administered by the Oklahoma Climatological Survey), a dataset now with a record length of ten years, radar data from the WSR-88D network, and Rapid Update Cycle (RUC) analyses to investigate the surface and environmental conditions (wind, pressure, thermodynamic, and precipitation features) accompanying MCSs with trailing, leading, and parallel stratiform precipitation; bow echoes; mesoscale convective vortices (MCVs); and MCSs that produce extreme rainfall. The Oklahoma Mesonet data, consisting of 5-min surface observations at about 30-km resolution, will enable detailed analyses of the mesoscale surface pressure fields. Particular attention will be focused on mesohigh/wake low couplets within MCSs. The intellectual merit of the research derives from the new understanding it will provide of the structure and physical processes associated with a broad range of mesoscale convective systems. The surface signatures of MCSs having different orientations of their stratiform precipitation regions (trailing, leading, and parallel), bow echoes, MCVs, and extreme-rain-producing MCSs have heretofore only been documented from a limited number of case studies. The ten-year record of Oklahoma Mesonet observations now affords the opportunity to more comprehensively determine the surface signatures of a large sample of such precipitation systems, from which inferences can be made about their dynamics. The broader impacts of the research relate to how it will improve understanding and ultimately prediction of MCSs and accompanying severe weather. The surface features associated with a large class of MCSs are measures, sometimes direct and sometimes indirect, of their severity and processes within the storms. For example, bow echoes are characterized by extreme surface winds, MCSs with trailing stratiform precipitation by mesohigh/wake low couplets, and certain extreme rain-producing storms by regeneration of new cells in the same location along storm-generated outflow boundaries. The recognition of such features in relation to the storms they produce is important to weather services for reliable nowcasting and short-term forecasting. These storms are responsible annually for significant life and property damage, and currently the forecast skill for them is low. This research is ultimately directed toward improving the skill in such forecasts.