A tornado is a "violently rotating column of air in association with a cumulonimbus cloud that is in contact with the earth's surface". One limitation of RADAR is that it can not tell the RADAR operator if the mesocyclonic circulation is in contact with the ground. The RADAR operator can only go by probabilities from the magnitude of the gate to gate shear. The only method of determining if the tornadic circulation is on the ground is through the use of a trained storm spotter. Another limitation of RADAR detecting tornadoes is due the earth's curvature. As a storm locates further from the RADAR site, it becomes more likely the RADAR beam will overshoot the mesocyclonic circulation. It is best to use a low tilt angle because the higher tilt angles have a higher probability of overshooting the mesocyclonic circulation. Also, a tornadic / mesocyclonic circulation can not be detected if in moves into the RADAR's cone of silence (conal region immediately above RADAR set). Still another limitation is beam spreading. The pixel size increases when moving further from the RADAR set. This decreased resolution makes it more difficult to identify mesocyclonic circulations that are displaced far from the RADAR. The resolution of a tornadic circulation erodes rapidly beyond 100 kilometers from the RADAR set. Due to the shallow nature and brief life span of land spouts and gustinadoes, RADAR can usually not pick up the circulation associated with these types of tornadoes. RADAR is very successful at being able to detect a mesocyclonic circulation especially if it is located between about 50 to 100 kilometers from the RADAR set. Within this range, the RADAR has a more likely chance of detecting the core of the mesocyclonic circulation since it occurs in the mid-levels of a supercell. Strong outbound velocities of at least 45 knots next to strong inbound velocities of at least 45 knots are used to infer a mesocyclone. Even with this identification, less than 30% of mesocyclones that trigger the alert on the Doppler RADAR produce a tornado. |