Details of colliding thunderstorm outflows as observed by Doppler lidar

Three cases of colliding outflow boundaries are examined using data collected from the NOAA Doppler lidar and a meteorological tower during the summer of 1986 near Boulder, Colorado. The data are unique because the lidar and the 300 m tower were colocated, providing measurements of both kinematic and thermodynamic properties. Lidar data reveal small-scale vortex roll instabilities within the leading edge of the outflow. Observations of the post-collision interactions showed that the warmer of the two outflows was deflected upward by the colder outflow to heights of 2 km. In all cases, this forced mechanical lifting was sufficient to produce convection. A simple model of two colliding density currents also suggests that deeper outflows are more efficient in initiating convection.