DUAL-DOPPLER AND MULTIPARAMETER RADAR OBSERVATIONS OF A BOW-ECHO HAILSTORM

During the afternoon and evening hours of 23 May 1991 a hail-producing multicellular severe thunderstorm developed near Denver, Colorado, an d tracked eastward for more than 100 km. Along this path, hailstone di ameters of 2-7 cm (0.75-2.75 in.) were reported at several points. The storm was observed by both the CSU-CHILL (CHL) and NCAR Mile High (MH R) 10-cm Doppler radars. The general echo morphology evolved by way of cyclic, discrete new cell formation near an outflow boundary moving a head of the storm's forward flank. As this new cell growth occurred, t he shape of the storm's most intense core also evolved in a periodic f ashion. On four separate occasions these cores briefly assumed a bow s hape with peak reflectivity values of 65-70 dBZ. The evolution of one such bow echo was examined by a series of six CHL-MHR dual-Doppler ana lyses. The resultant airflow patterns suggested that the core reflecti vity structure was deformed into the bowlike configuration by updraft- induced flow field perturbations. During the period covered by the dua l-Doppler analyses, dual polarization measurements made by the CSU-CHI LL radar were used to infer hail characteristics by placing the differ ential reflectivity (Z(DR)) and zero-lag cross correlation between hor izontally and vertically polarized echoes [rho HV(0)] observations in the context of the synthesized wind fields. These polarimetric data su ggest that the areal coverage of the hail and the diameter of the hail stones both maximized during the bow-echo phase.