SPC uses radar measurements (velocity) to detect rotation at different radar tilts. When you see 2 velocity points very close together, that usually raises the

SPC uses radar measurements (velocity) to detect rotation at different radar tilts. When you see 2 velocity points very close together, that usually raises the criteria to a warning. Sometimes, at the lowest tilt, we can detect debris on the radar.. But, as you said, not every warning translates into a confirmed tornado on the ground, a limitation of the current radar models.