Jim Steenburgh

(Utah State)

Mesoscale Forcing Lake Effect Precipitation over Lake Ontario and its Enhancement over the Tug Hill Plateau

When Apr 24, 2017
from 03:30 pm to 04:30 pm
Where 112 Walker
Contact Name David Stensrud
Contact email
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Jim Steenburg UtahImproved 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 mesoscale forcing of lake-effect precipitation and its enhancement over Tug Hill.  In contrast to contemporary conceptual models, which typically emphasize an invigoration (i.e., deepening and strengthening) of lake-effect convection over downstream terrain features, profiling radar observations from OWLeS indicate a 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 with long-lake-axis-parallel bands producing the highest precipitation rates, but the smallest relative increase in precipitation from lowland to upland regions.  In contrast, non-banded lake-effect periods exhibit smaller precipitation rates, but much larger relative increase in precipitation from lowland to upland regions.  These non-banded periods are more frequent and appear primarily responsible for the climatological lake-effect precipitation produced over Tug Hill.   Finally, interactions between the large-scale flow, shoreline geometry, and differential surface surface heating and roughness contribute to the development of mesoscale airmass boundaries along bulges in the south and southeast shoreline that extend downstream and contribute to the initiation of lake-effect systems over eastern Lake Ontario and their enhancement over Tug Hill.  Implications of these findings for operational forecasting and our understanding of lake-effect and orographic precipitation will be discussed.