The Impact of Microphysics Schemes in Convection-Allowing Simulations of Banded Snowfall

Banded snowfall events are associated with snowfall rates as high as 8 cm h-1, accumulations of snow exceeding 30 cm, and gradients in snowfall as large as 1 cm km-1. Because of these large gradients, large errors in forecast snowfall amounts can occur. Convection-allowing models offer the potential to improve the prediction of mesoscale bands of snow, as models with coarser grid spacing lack the ability to simulate the strength and width of the vertical circulation responsible for snowfall production. However, the amount and location of snowfall associated with mesoscale snowbands may be affected by the selection of the microphysics scheme. Each microphysics scheme makes assumptions about riming, fall velocity, and hydrometeor distribution, which can affect if and for how long snow is suspended within the updraft of a mesoscale circulation. This study examines how different microphysics schemes influence the evolution of mesoscale snowbands associated with winter storms in the central United States. Three banded snowfall events over the central United States have been simulated using the WRF-ARW with 3-km grid spacing. Forecasts of banded snowfall feature significant error growth of initial condition errors. Simulations lack some of this error, and thus allow for a more focused look into the role of microphysical processes in these events. Nine microphysics schemes which vary in sophistication and computational expense have been employed in each event simulation. For each event, the location of the mesoscale band of snow, the precipitation rate, the gradient in precipitation normal to the band, the width of the band, and precipitation amounts within the band will be examined. Objective comparison of each simulation with observations will be used to highlight any potential biases associated with different microphysics schemes.