Convective Rolls and Cells in Lake-Effects Snowstorms: Structures, Mechanisms, and Effects

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9510011 Hjelmfelt Mesoscale flows within convective boundary layers must be understood in order to fully determine the link between synoptic-scale circulations and surface characteristics. Observational evidence suggests that theoretical criteria are often unsuccessful in predicting the predominant mesoscale convective organization in the boundary layer. In particular, boundary layer flow structure knows as rolls are often observed when cellular convection is predicted. The proposed study seeks to employ both numerical and observational techniques to: (1) determine factors which control the development of boundary layer rolls in lake-effect snowstorms; and (2) determine how the mesoscale organization of convection influences mass overturning rates, precipitation rates, and boundary layer depth. The first goal will be accomplished by careful documentation of the three-dimensional structure of mesoscale convection near the eastern shore of Lake Michigan and how it varies with upwind atmospheric conditions and evolution of boundary layer winds, temperature, and moisture (ice, liquid, and vapor) profiles across the lake. Numerical simulations will be carried out over the range of observed conditions to give a more complete data set for determining the influence of wind shear, latent heat release, and other factors, on the organization of boundary layer convection. The influence of mesoscale convective organizations on mass overturning rates, precipitation rates, and boundary layer depth will be accomplished by carefully documenting how these features change near the downwind shore in both observations and simulations of rapidly changing mesoscale convective structure. This work is based on observations taken during the University of Chicago Lake Snow Project. Numerical aspects of this work will be carried out with the Advanced Regional Prediction System model developed at the Center for Analysis and Prediction of Storms at the University of Oklahoma . This research will be a collaborative effort between the Illinois State Water Survey and the South Dakota School of Mines and Technology. ***