Impact of initial environmental velocity profiles on numerical-model-based storm-scale analyses of the 4 May 2007 Greensburg, Kansas cyclic tornadic thunderstorm

It has been suggested that the onset of the Great Plains nocturnal low-level jet (LLJ) may have played a role in the intensification of the 4 May 2007 Greensburg, Kansas tornadic supercell, which produced at least 22 tornadoes (including two EF-3s and one EF-5) over a 7-hour period. In this study, we use an EnKF data assimilation framework to study the impacts of the initial environmental velocity profile on the early evolution of the Greensburg storm. In each experiment, reflectivity and velocity data from a WSR-88D and velocity data (only) from the University of Massachusetts mobile, X-band, dual-polarimetric Doppler radar are assimilated into a 48-member WRF model ensemble to simulate the storm in a horizontally homogeneous initial environment, one containing a LLJ and one not. The initial wind profile does not appear to exert much influence on the overall storm structure or observation-space diagnostics. The locations of the main supercell updraft and Greensburg tornado-like vortex are similar in both experiments. However, it is found that vortices generated in the environment containing the LLJ are deeper, more persistent, and more intense than those generated in the environment without.