Tuesday, 7 November 2006
Pre-Convene Space (Adam's Mark Hotel)
The Nebraska thunderstorm outbreak of 22-23 June 2003 is widely remembered for the Aurora supercell that dropped a record breaking hailstone and for the Superior supercell that produced the strongest measured mesocyclone in history. However, the storms' evolution into a mesoscale convective system (MCS) and its subsequent transformation into an elevated system (i.e. feeding on air parcels from above the boundary layer) has received far less attention. A north-south oriented line of several supercells was initiated on the evening of the 22nd in central Nebraska, on the western side of an outflow boundary from an MCS on the previous night. The storms subsequently evolved into an east-west oriented squall line throughout the evening, and became quasi-stationary along the Nebraska-Kansas border by the early morning hours of the 23rd. As a part of this evolution, the principal thermal boundary was also reoriented into the east-west direction. This east-west orientation occurred around the time that the MCS became an elevated system. Around 06Z the western part of the MCS abruptly began to move northward while the eastern part remained quasi-stationary. Our working hypothesis is that the MCS's propagation and triggering mechanisms changed once it became elevated. The discontinuity in motion between the eastern and western line segments may be due to a narrow southerly low level jet that interacted with the line's western end, or may reflect that the two line segments were ingesting air from two different source layers, leading to differing kinematic and thermodynamic properties.
The 22-23 June 2003 MCS was sampled by the Bow Echo and MCV Experiment (BAMEX). The excellent resolution of the BAMEX data provides an insightful look at this MCS as it transitioned to an elevated, nocturnal MCS. Dropsondes, GLASS soundings, regional wind profiles, and radar data will be analyzed and compared to real-world and quasi-idealized simulations using the Weather Research and Forecasting (WRF) Model. The goal of this investigation is a better understanding of how elevated convection evolves, is maintained, and propagates.
- Indicates paper has been withdrawn from meeting
- Indicates an Award Winner