A case example of the role of warm-sector convection in the development of mesoscale banded snowfall: 2003 November 22-24

Anecdotal evidence from National Weather Service area forecast discussions suggests that, in some instances, warm-sector convection may inhibit moisture transport to areas of snowfall further north. This study investigates the validity of this hypothesis using a three domain MM5 simulation, with grids of 36, 12, and 4 km. Convection in this case was severe, with winds as high as 70 kts and hail as large as 1 in. Snowfall amounts exceeded 10 in. First, physical processes involved in the production of mesoscale banded snowfall and the initiation and maintenance of convection will be discussed. Second, diabatic heating output from MM5 is used to compute a potential vorticity (PV) budget to investigate the diabatically generated low-level PV produced by convection. Third, the diabatically produced PV is isolated and inverted using a piecewise technique to analyze the effects of this PV anomaly on the large-scale flow. Lastly, a Lagrangian moisture budget is calculated along trajectories emanating from the convection to determine the impact of convection on northward moisture transport. In this case, convection does not inhibit the production of banded snowfall and serves to enhance some physical processes that lead to banded snow.