The inland evolution of lake-effect convection during landfall and orographic uplift as observed by profiling radars during OWLeS

A pronounced snowfall maximum occurs about 30 km downwind of Lake Ontario over the 600 m high Tug Hill plateau (hereafter: Tug Hill), a region where lake-effect convection is affected by mesoscale forcing associated with landfall and orographic uplift. Data from profiling radars deployed during the Ontario Winter Lake-effect Systems (OWLeS) field campaign (2013-2014) are used to characterize the inland evolution of lake-effect convection that produces the Tug Hill snowfall maximum. Four K-band profiling Micro Rain Radars (MRRs) were aligned in a transect from the Ontario coast onto the Tug Hill. Additional observations were provided by an X-band profiling radar (XPR).

Analysis is presented of a major lake-effect storm that produced snow accumulations of 6.4 cm liquid precipitation equivalent (LPE) over the Tug Hill. This event exhibited strong inland enhancement, with LPE increasing by a factor of 1.9 over just 15 km horizontal distance. MRR profiles reveal that this enhancement was not due to an increase in the depth or intensity of lake-effect convection. With increasing inland distance echoes become less intense, more uniform, more frequent, and less turbulent. This transition towards stratiform conditions may enhance snowfall rates by increasing precipitation frequency, decreasing hydrometer lofting, or enabling growth via a seeder-feeder mechanism. XPR observations reproduce the basic vertical structure seen by the MRRs but also reveal a suppression of snowfall below 600 m AGL upwind of the Tug Hill. Bulk statistics from 29 events demonstrate that the inland weakening of convection and transition to stratiform conditions are common features.