On the Forecast Sensitivity of MCS Cold Pools and Related Features to Horizontal Grid Spacing in Convection-Allowing WRF Simulations

While the implementation of convection-allowing models has improved the representation of convective features, a consensus is lacking regarding what horizontal grid spacing most appropriately resolves convective structures, is computationally feasible, and provides the most useful output to forecasters. The present study evaluates 14 simulated MCSs with 3-, 1- and 0.333-km horizontal grid spacing in order to understand sensitivity in simulated MCS forward propagation speeds and cold pool behavior with decreased grid spacing. MCS cold pools were found to be significantly larger in runs using finer grid spacing. In addition, a greater similarity in solutions occurred when grid spacing was refined to 1 km and less, with 1- and 0.333-km MCS cold pools more similar in magnitude, depth, length, and areal coverage, than 3-km cold pools. The 1-km simulations demonstrated a small increase in forecast skill for 3-h QPF throughout MCS evolution compared to 3-km runs. The 1-km MCS 9-h precipitation swaths were also better aligned with observations compared to 3-km simulations. When evaluating MCS forward propagation speeds, however, 3-km simulated MCS speeds were more similar to observations compared to 1 km.