584 The Impact of Microphysics Schemes in Convection-Allowing Models on the Prediction of Banded Snowfall

Tuesday, 24 January 2017
4E (Washington State Convention Center )
Philip N. Schumacher, NWS, Sioux Falls, SD; and D. M. A. Baxter

Banded snowfall events are associated with snowfall rates as high as 8 cm h-1, accumulations of snow exceeding 30 cm, and large gradients in snowfall as high as 1 cm km-1. Because of these large gradients, large errors in snowfall amounts can occur. To improve prediction of mesoscale bands of snow, convection-allowing models (CAMs), which have a grid spacing of 4 km or less, could be used. Past research has shown that CAMs can be used to provide better forecasts for severe convective weather because they can provide a better simulation of convective updrafts and downdrafts. Since updrafts associated with mesoscale bands of snow can have a width of less than 50 km, CAMs may better simulate the strength and width of the vertical circulation than lower resolution models such as the Global Forecast System (GFS) and improve forecasts of the location and amount of snowfall. However, the amount and location of snowfall associated with mesoscale bands of snow 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 influences the evolution and prediction of mesoscale bands of snow associated with winter storms in the central United States. Several cases of banded snowfall over the central and eastern United States will be simulated using the WRF-ARW with 3-km grid spacing. Each case will be simulated six times with the same initial conditions but different microphysics schemes. For each case, 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. Comparison of each simulation with observations will be used to highlight any potential biases associated with different microphysics schemes.

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