Misovortices and Boundaries within Long Lake-Axis-Parallel (LLAP) Lake-effect Snow Bands East of Lake Ontario during the 20132014 Ontario Winter Lake-effect Systems (OWLeS) Project

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Thursday, 8 January 2015: 11:30 AM
224A (Phoenix Convention Center - West and North Buildings)
Jake Mulholland, University of Illinois, Urbana, IL; and J. W. Frame and S. M. Steiger

Recent field studies on lake-effect convection in the eastern Great Lakes region (e.g., LLAP 2010-2011 and Ontario Winter Lake-effect Systems; OWLeS 2013-2014) have revealed the presence of misovortices with diameters between 40 m and 4000 m within long lake-axis-parallel (LLAP) bands. These misovortices usually develop along horizontal shear within these bands. In some instances, the wind shifts are located on the northern edge of the west-to-east oriented bands, whereas in other cases, the convergence boundaries were found in the middle or along the southern edge of the bands. In most of these cases, the shear zone is collocated with a sharp horizontal gradient in reflectivity and is found on the side of the band closest to the shore of Lake Ontario.

One of the cases from the OWLeS project featured a boundary that originated within the middle of the snow band and propagated southward through the band. Locations on the south shore of Lake Ontario, such as Oswego, NY, experienced a drop in surface temperatures of 1-2C in less than 15 minutes with the passage of this boundary. This boundary may be similar to a gust front, only the cold outflow behind can be attributed to sublimation, not evaporation.

While it is likely that the misovortices form owing to horizontal shear instability along the low-level convergence zones in the bands, it is uncertain as to why the convergence boundaries and shear zones form. It is possible that the broader region of low-level convergence associated with the secondary circulation plays a role. Upper-air soundings, surface mesonet transects, mobile Doppler radar data, and microwave profiling radiometer data will be analyzed and presented to determine the crucial processes involved in the formation of these convergence boundaries and low-level cold pools. Boundary-layer wind direction and speed will also be analyzed to determine on which side of the band the greatest low-level convergence exists and whether this is a factor in the location and movement of these boundaries.