Analysis and Prediction of 8 May 2003 Oklahoma City Tornadic Thunderstorm and Embedded Tornado using ARPS with Assimilation of WSR-88D Radar Data

The parental supercell storm of the 8 May 2003 Oklahoma City tornado is successfully simulated starting from an initial condition that has assimilated the Oklahoma City WSR-88D radar data. High-frequency intermittent analysis cycles are performed using the ARPS 3DVAR and cloud analysis combination on a 1-km horizontal resolution grid to obtain quality analyses for an initial time before the tornado outbreak. Four such experiments are conducted to study the impact of radial velocity data in addition to those of reflectivity and the impact of a mass-divergence constraint in the 3DVAR cost function on the supercell storm forecast. It is found that the additional use of radial velocity plays a critical role in the establishment of the mesocyclone during the forecast period.

A 100-meter resolution grid is nested within the most successful 1-km forecast, starting from the 1-km initial condition interpolated to the 100-meter grid. Within this 100-m grid is another 50-m grid further nested down to capture even finer scale structures associated with the tornado. The 100 and 50 meter forecasts lasted for 1 hour and 40 minutes, respectively, long enough to cover the entire period of the tornado outbreak. Both high-resolution grids are able to produce tornadoes of F1-F2 intensity in the model, near the time and location of the real tornado outbreak. The predicted tornado track is within 10 km of the observed one. Detailed analysis of the tornado structure in the model and direct comparisons with radar observations will be presented.