Polarimetric radar data of two microburst-producing thunderstorms are examined. Very high local values of specific differential phase are found to coincide with the first appearance of a divergent low-level radial velocity signature. Considered along with high reflectivity factor and low differential reflectivity values, this indicates the bulk presence of a hail and rain mixture within the downdraft column. These observations are corroborated by a decrease in the correlation coefficient toward the ground, indicating an increasing mixture of hydrometeor types. Previous modeling and wind tunnel studies state that melting hailstones form a water torus during their descent, with frequent shedding of water drops of various size. Bulk hydrometeor characteristics deduced from these polarimetric radar observations are compared to these model and wind tunnel studies. It is surmised that diabatic cooling due to the phase change of melting hail is a large contributor to the development of these microbursts.