Upwind Coastline-induced Downdrafts and Influence on Growth of the Lake-effect Convective Boundary Layer
One of the objectives of the Ontario Winter Lake-effect Systems (OWLeS, https://www.eol.ucar.edu/field_projects/owles) field project, conducted during December 2013 and January 2014 in the vicinity of Lake Ontario, was to determine the processes by which upwind lakes modify boundary layer and snow growth rates over Lake Ontario. This presentation will focus on the 28 January 2014 case, when lake-effect clouds and snow extended northeastward from Lake Erie toward Lake Ontario. Observations from several university-owned radiosonde systems, University of Wyoming King Air in situ instrumentation, Wyoming Cloud Radar (WCR), and NOAA operational sites are used to examine the details of changes in the PBL as the air moves from snow-covered land surfaces to Lake Ontario waters.
A mesoscale stationary region of decreased cloudiness and snowfall rates, and lower PBL tops was evident from about 5 km upwind of the Lake Ontario shoreline to about 10 km downwind. Superimposed on this were intense local downdrafts resulting in local sharp decreases in the depth of the PBL, identifiable by downward penetration of stable above-boundary layer air. These local downdrafts are inferred, based on WCR observations, to be consistently present, but not spatially stationary. Implications of these mesoscale and smaller-scale downdrafts on convective growth over Lake Ontario will be discussed.