3A.1 Investigation of Hydrometeor Lofting During Banded Snowfall Events

Monday, 4 June 2018: 1:30 PM
Colorado A (Grand Hyatt Denver)
Gary M. Lackmann, North Carolina State Univ., Raleigh, NC

The synoptic-scale and mesoscale environments of banded snowfall events often feature strong mid-level frontogenesis accompanied by weak symmetric stability. Previous observational and numerical studies document the occurrence of upward vertical velocities in excess of 1 m s-1 in these winter storms, suggesting that lofting of snow could affect snowfall distribution. Here, I present an update to previous work that investigates this phenomenon, aiming to test the hypothesis that the lofting of snow plays a significant role in determining the intensity and in some cases the spatial variation in snow accumulation.We have added diagnostic variables to the Thompson microphysics scheme in the WRF model, allowing direct output of the mass-weighted fall velocity of snow, and also the vertical snow flux. These diagnostics demonstrate the degree to which snow is lofted in banded winter storms, and also demonstrate potential operational value. Additionally, experiments were conducted in which the terminal fall velocity of snow was altered (increased and decreased below the default value). These experiments allow an evaluation of the extent to which lofting contributes to heterogeneity in surface snowfall accumulation. Results demonstrate that lofting is taking place, as an upward snow flux is simulated at sufficiently high resolution. Here, two additional case simulations are presented, with the goal of documenting the ubiquity and variability in this phenomenon during both banded and non-banded snow events. One event took place over North Carolina in early 2018, featuring banded snowfall. Another case, from December 2008, did not exhibit banded snowfall. Contrasting these events clarifies the role of lofting in snowfall events.
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