IMPROVEMENT OF THE WSR-88D MESOCYCLONE ALGORITHM

The build 9 Weather Surveillance Radar-1988/Doppler mesocyclone algori thm (B9MA) is designed to locate mesocyclones [rotating thunderstorm u pdrafts with diameters between 1.8 and 9.2 km (1-5 n mi)]. Because the re is less than a one to one correspondence between tornadoes and meso cyclones, the B9MA alerts forecasters when it detects circulations tha t meet its criteria but tornadoes may not be observed. On the other ha nd, some tornadoes are not accompanied by large-scale mesocyclonic cir culations. Weather radars cannot resolve small-scale tornadic circulat ions, and the B9MA may fail to alert forecasters that a tornado is pre sent. The B9MA is only one of many tools that forecasters should use t o predict tornado formation. This paper describes limitations of the B 9MA and how to improve its performance. The correlation between algori thmic detections and severe weather occurrence may be optimized under the premise that storms with strong, deep rotations are more likely to be associated with severe weather. Some tornadic circulations missed by the B9MA can be detected when the value of threshold pattern vector , a B9MA adaptable parameter, is lowered. When a rotational strength f ilter is added to the program logic, some algorithm detections of nont ornadic mesocyclones can be eliminated.