Radar Tutorial
Chapter 1, Page 7: Hook Echo
If the cell has significant enough rotation, a small hook in the radar image may develop on the southwestern flank. In
the field, this will be visible as rain and/or hail wrapping around the rain-free base area. This was the only way to
"see" possible tornadoes via radar before NEXRAD. One of the two cells above produced the tornado in Fort Smith, AR
on 4/21/96.
The tornado, if it exists, will likely be visible from the south or southeast of the storm, where the inflow rushes
into the "slot" in the "rain-free" base area. The "hook" indicates cool out-flow air and rain wrapping around the
in-flow slot at the rear of the rotating thunderstorm. This is called "rear flanking downdraft" (RFD). Notice in the
accompanying examples some of the heaviest rain occurs immediately adjacent to the rain-free base and in-flow slot.
This is characteristic of a potentially tornadic supercell.
Microbursts with resulting severe straight line winds can occur in the RFD as well as the down draft or rain area of
the storm.
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