Assimilation and Forecasting of a Supercell Storm: Simulated and Observed Data Experiments

Radar data assimilation and forecasting experiments have been performed on a tornadic supercell that occurred during the CASES experiment near Wichita, Kansas in May of 1997. This supercell developed in an environment of strong shear and moved at approximately 30 degrees to the right of the mean wind (measured between the surface and 5 km). The goal of this study is to examine the mechanisms that control the motion and evolution of this storm.

The primary data source used in this study is the WSR-88D radar located near Wichita. Radial velocity and reflectivity have been assimilated into a storm-scale model using the adjoint technique. This technique allows the incorporation of data spaced over time which is important for capturing the evolution of the storm. It is shown that the motion of the storm is strongly controlled by the cold pool that develops at low levels. In turn the strength of this cold pool is determined by the evaporation rate which can be retrieved by the 4DVar data assimilation technique.

At the Conference we will present a number of assimilation and forecasting experiments that have been performed on this supercell. We will also compare and contrast these numerical forecasts with traditional storm forecasting techniques that are based largely on extrapolation.