The Influence of Turbulence Parameterizations on the 2 March 2018 Snowstorm

Sub-grid scale turbulence in WRF is handled by planetary boundary layer (PBL) parameterizations. These schemes attempt to represent turbulent mixing processes occurring below the resolvable scale of the model grid, and act upon temperature, moisture, and momentum in order to produce a more realistic representation of the low-level atmospheric structure. In addition, more sophisticated schemes may alter cloud water and/or replicate the effects of radiationally driven cloud-top mixing. During a precipitation event, the modifications to temperature, moisture, and momentum fields by the PBL scheme may influence precipitation strength and, particularly in the cool-season, precipitation type. Given the diversity of PBL physics options available to the NWP community, we look to investigate the influence of various PBL schemes on a cool-season mixed-precipitation event.
This study uses the Weather Research and Forecasting model, run at convection-permitting resolution, to examine the effect of PBL mixing on the extent and character of precipitation generated from the 2 March 2018 snowstorm impacting the northeastern US. Accumulated boundary layer tendencies of potential temperature, moisture, and wind suggest the parameterized mixing applied by various PBL schemes can have a substantial impact on mesoscale precipitation location and type. In addition, PBL schemes with common lineages and theoretical underpinnings, such as the GFS and YSU schemes, can produce markedly different thermal profiles and precipitation types for the same initial conditions. This study explores why PBL schemes using similar theoretical assumptions produce differing thermal profiles and resulting precipitation fields.