The Enhancement of Lake-Effect Precipitation over the Tug Hill Plateau during the Ontario Winter Lake-effect Systems (OWLeS) Field Program

Improved understanding of the influence of orography on lake-effect storms is crucial for weather forecasting in many lake-effect regions. During December 2013 and January 2014, the National Science Foundation sponsored Ontario Winter Lake-effect Storms (OWLeS) field program examined lake-effect storms in the vicinity of Lake Ontario, including their enhancement over the Tug Hill Plateau (hereafter Tug Hill), which rises 500 m above lake level and experiences some of the most intense snowstorms in the world. This presentation provides an overview of key OWLeS-derived findings related to the enhancement of lake-effect precipitation over Tug Hill. In contrast to contemporary conceptual models of lake effect interacting with downstream orography, which typically emphasize an invigoration of lake-effect convection (i.e., deepening and strengthening) over downstream terrain features, profiling radar observations from OWLeS indicate an overall decrease in echo depth, decrease in turbulence, and increase in the frequency and uniformity of radar echoes over Tug Hill, consistent with a convective-to-stratiform transition. Significant variations in precipitation enhancement with lake-effect mode have also been identified. For example, strongly organized long-lake-axis parallel bands produce the highest precipitation rates but the smallest increase in precipitation from lowland to upland locations. In contrast, non-banded lake-effect periods exhibit smaller precipitation rates, but much larger increases in precipitation from lowland to upland locations. Although precipitation rates are weaker, these non-banded periods are more frequent and appear to be primarily responsible for the climatological precipitation maximum produced over Tug Hill. Implications of these findings for operational forecasting and our understanding of lake-effect and orographic precipitation will be discussed.