Anatomy of a Supercell:Tuscaloosa EF4

The supercell thunderstorm in the radar picture above contains a hook echo(white arrow). A hook echo is the radar signature of precipitation wrapping around a mesocyclone, the rotating column of air within the storm. The area with no precipitation is also known as the bounded weak echo region, or BWER (red arrow). The updraft is so strong in the area of rotation that the rain and hail cannot fall, and have been blown to the southwest (blue arrow), where the rear flank downdraft is (green arrow). Typically this precipitation is only present to the north, but not in this case. From the west, the area of the mesocyclone would be shrouded by rain and hail. The clear mesocyclone is where a tornado may, and in this case does, form. The entire storm moves northeast toward the upper right corner of the radar screen, the mesocyclone or tornado trailing with it. Storms with a hook echo are guaranteed to be tornado warned, it is not just a matter of spotting one forming or on the ground. This is the Tuscaloosa, Alabama storm that spawned a massive EF4, shown by the hook echo above.