Mesoscale Forcing of Lake-Effect Precipitation over Lake Ontario during OWLeS IOP2b

Long-lake-axis-parallel (LLAP) lake-effect precipitation systems that form when the flow is parallel to the long axis of an elongated body of water frequently produce intense snowfall.  Conceptual models of these LLAP systems typically emphasize the role of thermally forced land-breezes from the flanking shorelines, with low-level convergence and ascent centered near the lake axis.  In reality, other factors such as coastal geometry and differential surface roughness can strongly influence LLAP systems. Here we use WRF-model simulations to examine the mesoscale forcing of a LLAP system over Lake Ontario during IOP2b of the Ontario Winter Lake-effect System (OWLeS) field campaign.  In these simulations, the lake-induced mesolow, shape of the Lake Ontario shoreline, and differential surface heating and roughness contribute to the development of three major convergence zones. The first forms near the south shoreline bulge between St. Catharines, ON and Rochester, NY, extends downstream and ultimately along the long-lake axis over eastern Lake Ontario, and plays a primary role in the LLAP-system development.  The second forms near the irregular north-shore peninsula at Prince Edward, ON, and contributes to the intermittent development of a secondary snowband.  The third forms near the southeast shore, extends obliquely across the LLAP-system near Tug Hill, and influences inland precipitation processes.  These results highlight the multifaceted nature of LLAP-system development over Lake Ontario, including the orientation of the flow relative to subtle variations in the shoreline geometry, and may be applicable to the understanding and prediction of lake-effect precipitation generated by other bodies of water.