P74 Prediction of Convective Morphology in Near-cloud Permitting WRF Model Simulations

Convection-permitting horizontal grid spacings are being used increasingly often for operational forecasting. These simulations often depict convective structures similar to those that have been observed in radar data (e.g., Kain et al. 2008). However, although some studies have suggested that there is value in how these runs depict convective modes (Weisman 2008), others have identified problems in the forecasts (e.g., Fowle and Roebber 2003, Done et al. 2004). Accurate prediction of convective mode could help forecasters since mode is related to severe weather (e.g., Gallus et al. 2008). However mode has been shown to not only depend on larger-scale parameters such as instability and shear, but also on localized variations in these parameters (French and Parker 2008) or the presence of boundaries (Schumann and Roebber 2010). Rapid evolution from cells into a linear system can occur if mid-level flow is approximately parallel to a surface boundary due to merging cold pools (Dial and Racy 2004). Weisman et al. (1988) and Weisman (1992) showed the shear affects the tilting of the updrafts, and in turn, extent of stratiform rain. How fast cellular systems become linear positively correlates with deep-layer forcing, moreso than the orientation of the wind vector in the cloud layer (Dial et al. 2010). In the present study, the WRF model is used to simulate 37 cases with 3 km horizontal grid spacing to better understand the ability of the model to accurately depict convective mode and its evolution. An objective skill measure is defined and used to compute scores for each case. In addition, largerscale parameters are examined to see if they can be used to get an idea of the skill with which the WRF model will likely predict mode on a given day. ___________________________________________ Corresponding author address: William A. Gallus, Jr., ISU, 3010 Agronomy Hall, Ames, IA. Email: [email protected]. 2. Data and Methodology