5 Utilizing a Semi-idealized Modeling Framework to Understand Meso- and Convective-scale dynamics of severe Lake-effect Snowstorms

Monday, 3 August 2015
Back Bay Ballroom (Sheraton Boston )
Adam K. Massmann, University at Albany, Albany, NY; and J. R. Minder

The Buffalo lake-effect snowstorm (LES) of November 2014 caused 13 deaths, closed I-90, and required a National Guard deployment to secure the safety of residents. The areas of highest impact were located on the northern end of the snow band where an observer-described “wall of snow” dropped 1.5 m of snow mere kilometers south from areas receiving tens of centimeters of snow. The large gradients in reflectivity and snowfall rates on the northern edge of the band contrast sharply with the weak reflectivity gradients and gradual tapering off of snowfall rates on the southern edge of the band.

The Weather Research and Forecasting Model is used within a semi-idealized modeling framework to investigate what modulates intensity, location, and cross-band asymmetry of precipitation in events such as this. Convection-allowing resolution and a sophisticated microphysical parameterization represent key LES processes while simplified initial and boundary conditions allow for controlled manipulation of model state-space and facilitate testing of specific hypotheses. Mesoscale experiments with horizontal grid resolutions of O(1000m) explore how background flow, lake geometry, terrain, and mesoscale convergence interact to control surface precipitation patterns. Low-level sublimation and preferential advection of hydrometeors by the cross-lake component of the geostrophic wind do not drive cross-band asymmetry. However, the interaction of cross-band asymmetry in the low-level wind field with lake-triggered convection may be a primary control on outflow dynamics and band asymmetry. Mesoscale experiments are supplemented by higher resolution simulations (O(250m)) to provide further insight on the interplay between sub-band convective features and mesoscale dynamics, and test the sensitivity of model results to horizontal resolution.

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