and extending over a deep layer of the thunderstorm, not the actual tornadic circulation. The TVS is, however, indicative of a likely tornado or an incipient tornado. The couplet and TVS typically precede tornado formation by 10–30 minutes but may occur at nearly the same time or precede the tornado by 45 minutes or more. Polarimetric radar can discern meteorological and nonmeteorological and other characteristics of hydrometeors that are helpful to tornado detection and nowcasting. Nonmeteorological reflectors co-located with a couplet, can confirm that a tornado has likely occurred and lofted debris. An area of high reflectivity, or debris ball, may also be visible on the end of the hook. Either the polarimetric data or debris ball are formally known as the tornado debris signature (TDS). The hook echo feature is formed as the RFD occludes precipitation around the mesocyclone and is also indicative of a probable tornado (tornadogenesis usually ensues shortly after the RFD reaches the surface). After the implementation of the WSR-88D network in the U.S., the probability of detection of tornadoes increased substantially, the average lead time rose from four minutes to thirteen minutes, and a 2005 NOAA report estimates that as a result of improved warnings that there are 45 percent fewer fatalities and 40 percent fewer injuries annually. Dual-polarization radar, being implemented to the US NEXRAD network, may provide enhanced warning of tornadoes and severe winds and hail associated with the hook echo due to distinct precipitation drop characteristics. Polarimetric radar boosts precipitation observation and prediction, especially rainfall rates, hail detection, and distinguishing precipitation types. Proposed radar technologies, such as phased array and CASA, would further improve observations and forecasts by increasing the temporal and spatial resolution of scans in the former as well as providing low-level radar data over a wide area in the latter. In certain atmospheric environments, wind profilers may also provide detection capabilities for tornadic activity. Hail, downburst and downpour Hail forms in a very intense updraft in a supercell or a multicellular thunderstorm. As for tornadoes, BWER detection and a tilted updraft are indicative of that updraft but does not lead to predict hail. The presence of a hail spike in the reflectivity pattern is an important clue. It is an area of weak reflectivity extending away from the radar immediately behind a thunderstorm with hail. It is caused by radiation from the radar bouncing from hailstone to hailstone or