Significance of environmental vertical wind shear in convective upscale growth: Observations and model analyses

Environments conducive to deep convection were sampled during the Mesoscale Predictability Experiment (MPEX). These environments include both those of mesoscale convective systems (MCS) and discrete supercells. Previous studies have concluded strong deep-layer shear favors discrete modes while dominant low-level shear supports rapid upscale growth. A four-day sequence in late May 2013 included a variety of convective modes observed using upsondes by MPEX participants. These events were modeled using a 36-member nested version of the Weather Research and Forecasting Model (WRF). Observations (including surface and radar) were assimilated using an ensemble Kalman filter (EnKF) provided by the Data Assimilation Research Testbed (DART). Several supercells initiated along a dryline on 28 May 2013 in the Oklahoma Panhandle and southern Kansas with MPEX participants sampling the downstream environment of a targeted cell. Ensemble mean analyses consistently underestimate the magnitude of 3-10 km shear with convection reducing shear magnitudes along the dryline while enhancing shear in the inflow region. However, some ensemble members accurately depict 3-10 km shear. The ensemble forecast tends to favor rapid upscale growth in members with significantly underestimated 3-10 km shear while members with large 3-10 km shear retain a more discrete mode. Two MCSs developed in the Texas Panhandle and western Oklahoma on 29 May followed by two days of supercells in central Oklahoma. Experiments (previously described) will compare upper shear analyses, observations, and their forecast implications.