One of the most difficult local mesoscale forecasting problems in south-central Texas has been the timely issuance of flood watches and warnings. The purpose of this project is to increase understanding and the ability to interpret precipitation products generated by the WSR-88D radar in order to improve the hydrology aspects of forecasting.
During a recent NWS/Texas A&M field program, twenty different convective storm systems were jointly sampled using both the WSR-88D and the Texas A&M University's 10-cm Doppler radar (ADRAD). Using the reflectivity data obtained from each radar, the storm structure for one case study is being investigated to determine the possible effect of the WSR-88D's radar beam geometry on the performance of the precipitation algorithm at ranges in which the ADRAD was better able to sample the storm system.
Currently, at the NWS office in Houston, the WSR-88D precipitation algorithm makes use of the radar reflectivity only--rain gage data are not included. Since strong vertical and horizontal gradients in radar reflectivity often exist in convective storms and since the cross-sectional area of radar beams increases rapidly with range, it is believed that the WSR-88D precipitation algorithm's performance will be strongly dependent on the range of the storm from the radar site. Consequently, it may be possible to have significant differences between estimated precipitation amounts and those that are actually observed. Since it is believed that the vertical and horizontal gradients of convective storms are similar in other parts of the United States, the research activities conducted here may have wide application and may lead to new techniques in interpreting radar reflectivity and precipitation accumulations as determined from WSR-88D data.
Problems with the calibration of the ADRAD resulted in a temporary loss in the ability to measure calibrated reflectivity data. Consequently, the project has been extended until the problems have been resolved.