Sensitivity of Simulated Drylines to Boundary Layer Parameterization and Grid-Spacing

One of the biggest challenges facing the current generation of high-resolution numerical weather prediction models is accurately depicting the boundary layer, which has direct impacts on forecast sensible weather like low-level temperature, moisture, and winds, as well as instability and convection initiation. The dryline, an inherently boundary layer phenomenon, has long been acknowledged for its role in convection initiation during springtime in the central United States. Previous studies have shown that 24-h forecasts of dryline position in a 4-km grid-spacing WRF model were associated with large eastward biases when compared to the corresponding RUC analysis field. One hypothesis presented is that the high-resolution simulations tended to over-mix the boundary layer, causing the dryline to propagate too far east. With that in mind, the purpose of this paper is to attempt to address the following research questions:

1) Will more advanced boundary layer parameterization schemes yield better predicted drylines in high-resolution models? 2) Does decreasing the horizontal grid-spacing have an adverse effect on simulated drylines?

Several sensitivity tests will be presented for three dryline case studies (10 May 2010, 24 May 2011, and 14 April 2012). These “tornado-outbreak” cases were selected for their relevancy to convective forecasting.