Dual-Doppler Observations of Boundaries, Vortices, and Varying Band Morphology in the Long-Lake Axis Parallel Snow Band of 10-11 December 2013 During the Ontario Winter Lake-effect Systems (OWLeS) Project

On 10-12 December 2013, a long-axis parallel (LLAP) lake-effect snow band formed over Lake Ontario and affected regions east of the lake, including the Tug Hill Plateau. This band was sampled by the assets of the Ontario Winter Lake-effect Systems project, including the University of Wyoming King Air Aircraft, the University of Alabama in Huntsville Mobile Integrated Profiling System, five rawinsonde systems, three mobile Doppler radars, two mobile mesonet vehicles, and eight portable weather stations.

At the beginning of mobile Doppler radar observations, just after 0000 UTC 11 December, the band was a solid, intense, LLAP band. The mobile Doppler radar data reveal the presence of a 1-km deep east-west oriented wind shift within the band during this period, along which a horizontal shear zone and numerous vortices were observed. Vertical motion was also enhanced along this boundary, owing to low-level convergence, so it was likely that vortex stretching further intensified these vortices. The band shifted southward in response to a passing shortwave trough within the first two hours of Doppler radar observations. Additionally, synoptic and mesoscale observations, along with in-situ thermodynamic observations are presented to ascertain characteristics of this boundary, including its likely type. Following the passage of the shortwave trough, the band shifted northward again and became broken and dominated by individual convective elements. Following this transition, the horizontal shear zone disappeared, the number of vortices decreased dramatically, but yet isolated vortices continued to be observed. A series of dual-Doppler wind syntheses are presented that document the life cycle of one of these vortices. Unlike the earlier vortices, this vortex did not form along a significant preexisting wind shift, but instead was located beneath one of the stronger convective cores in the band, again implying that vortex stretching played a role in its intensification and maintenance.

The band resolidified during the afternoon of 11 December as a secondary 500-hPa shortwave trough approached the region, resulting in a higher inversion height and thus a deeper convective boundary layer. Doppler radar data will also be examined during this period to investigate the presence of horizontal shear zones and vortices.