Doppler Lidar Observations of the Vertical Velocity Preceding Thunderstorm Outflow over the Great Plains

Previous studies of the velocity field of thunderstorm outflow have not focused on vertical velocity in advance of the outflow interface. Doppler LiDAR provides the capability to observe the vertical velocity field prior to, during, and following the passage of a thunderstorm’s outflow. Between 17 May 2019 and 15 June 2019, a team from the National Severe Storms Laboratory (NSSL) and the Cooperative Institute for Mesoscale Meteorological Studies from the University of Oklahoma (OU CIMMS) collected mobile LiDAR data as a part of the Targeted Observations by Radar and UAS of Supercells (TORUS) field project. The ideal deployment position was just south of the supercell mesocyclone. Data collected from this location provided cases of thunderstorm downdraft; either an outflow or a rear flank downdraft (RFD). Data were collected using an alternating strategy of horizontal VADs every three minutes with vertical stares in between.

A persistent strong updraft of up to 10 m/s was noted within the boundary layer prior to the arrival of the downdraft feature. The purpose of this presentation is to display vertical velocity data collected in the vicinity of these downdraft features and classify the cases by whether they more closely resemble outflow and RFD by evaluating thermodynamic data from collocated mobile mesonet observations and WSR-88D radar data. These classifications will be used to establish differences in the preceding vertical velocity between the two downdraft classifications. Based on analysis of these observations, research questions will be developed about the variability of pressure perturbations, static stability, total duration of the pre-downdraft ascent, and their interconnections. In future work, these research questions will be addressed via idealized simulations to understand the parameters that control these updrafts.