Rear flank downdraft

The rear flank downdraft (RFD) is a region of dry air wrapping around the back of a mesocyclone in a supercell thunderstorm.

[3][4] Firstly, the initial rear flank downdraft is air from aloft transported down to the surface by colliding and mixing with the storm.

Some observations showed the presence of an enhanced downdraft in the vicinity of the strongest low-level rotation, behind the main storm updraft.

Many researchers have realized that rear flank downdrafts, especially those associated with hook echoes, are fundamentally critical to tornado formation (tornadogenesis).

Furthermore, observations of the clear slot during and just prior to the tornadic stage, imply the air infiltrating the tornado may come from the RFD.

Regularly, generation of large vertical vorticity close to the surface in an environment which is required for tornadogenesis, is attributed to downdraft.

Tornadoes may arise, however, in the absence of a downdraft in environments containing preexisting vertical vorticity at the surface, such as in some cases of nonsupercell tornadogenesis.

Air circulation in a supercell thunderstorm, including the rear flank downdraft
A classic hook echo, indicating the presence of a rear flank downdraft (and in this case, a tornado). The tornado associated with this echo was part of the May 2003 tornado outbreak sequence .