In this study, we apply a modified version of the WRF (Weather Research and Forecast) 3DVAR system to the 12-13 May 2005 precipitation case over the Central Great Plains, by assimilating data from six WSR-88D radars. Instead of assimilating reflectivity data in dBZ directly, we derive hydrometeor mixing ratios for rainwater from the reflectivity on the condition above 0 degree C. Moreover, we use the simplified constrained gamma function for the rain drop size distribution. Therefore, rain microphysics is also based on that distribution and the modifications of rain-related terms like cloud water and temperature are also related to that distribution.
Ten-minute analysis cycles are performed over a one-hour assimilation window, on a 4 km grid nested within the outer domain with a 20 km grid. Forecasts are performed from the resulting analysis and the results are compared with runs without the use of radar data, and with the direct assimilation of reflectivity.
Supplementary URL: