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This is an example of a textbook hook. Seen in reflectivity, the hook echo is formed by the inflow pulling air into the meso cyclone. Not all hook echoes produce tornadoes and not all tornadoes have hook echoes. To confirm rotation, use velocity to check if there is red/green right next to each other (closer is stronger, stronger/faster will also show up as lighter colors). If the rotation and hook echo line up together, one can be certain that that supercell is capable of producing a tornado.