Frequency, Origin, and Implications of Elevated Mixed Layers Upwind of the Great Lakes

Lake effect storms have a significant impact every year on over 30 million people living in the Great Lakes region. Considerable research has shown that conditions on the upwind side of a lake play a large role in the development of lake effect storms that produce snow on communities located near downwind shores. For example, lower static stability near the upwind shore generally contributes to deeper lake-effect boundary layers and increased snow. Influences of the vertical structure of static stability upwind of a lake have received much less scientific attention. In particular, the few studies in journal literature on this topic indicate that lake-effect storms may grow rapidly over a lake if they penetrate elevated mixed layers (EMLs), but the subsequent influences on lake effect snowfall haven’t been quantified observationally.

We analyzed several atmospheric variables from NOAA sounding data taken in a central location in the Great Lakes, DTX (White Lake), Michigan, as a way of determining the presence of EMLs during the Ontario Winter Lake-effect Systems (OWLeS) field campaign (December 2013 - January 2014, conducted over Lakes Erie and Ontario). We define an elevated mixed layer as having a nearly constant equivalent potential temperature ([Equation]) that is decoupled from the surface. Our findings show that elevated mixed layers occur more frequently in the region typically upwind of Lakes Erie and Ontario in lake-effect situations than previously thought. Additionally, we analyzed the relationship between the presence of EMLs and lake-effect boundary layer presence, boundary layer depth changes across the lakes, and proximity to low-pressure systems. Careful analyses suggest that mixing between the lowest EML and the lake-effect boundary layer leads to increased snowfall on the downwind shore. Going forward, we plan to analyze EML frequency upwind of the entire Great Lakes region during the winter of 2013-2014, in order to provide insight into possible modes of EML formation discussed in the literature. Results will be presented showing how EML frequency upwind of the Great Lakes region compares to that over Lakes Erie and Ontario.