Conventional Doppler radar sends out a horizontal energy pulse providing a one‐dimensional view of precipitation. Dual pol radar sends both horizontal and vertical pulses, providing a two‐dimensional view. Thus, it provides much better information about the size, shape, and estimated amount of precipitation, distinguishing between rain, snow, and hail. Basic dual pol products include correlation coefficient (CC), differential reflectivity (ZDR), and specific differential phase (KDP). More information is available on our Dual Pol webpage.
High reflectivity was present in a supercell on March 2, 2012 over central Kentucky (upper left; white arrow). Here, ZDR (upper right) showed low values (white color) indicating spherical shapes suggestive of large hailstones. CC (lower right) showed values of 0.8-0.95 (yellow/green) indicative of a combination of large hail and wet hail/rain. KDP (lower left), which helps assess rain drop size/density, showed a small black area (data dropout), surrounded by values of 1-3 (blue-green). This also denoted large hail, surrounded by small hail and large drops. Thus, dual pol clearly identified large hail in the storm, which produced at least golf ball size. Reflectivity alone (upper left) suggested large hail, but could not confirm it as high values can also mean a lot of small hail and/or a hail/very heavy rain mix.