Radar Tutorial
Chapter 2, Page 2: More Velocity Radar
Here is a beautiful image of a hook echo courtesy of the National Weather Service MPX Field Office. This event
occurred September 18, 1997 over eastern Morrison County. At the time of this image, this cell was producing a
tornado and doing F3 level damage fortunately in a rural area. This cell produced several tornados in Morrison,
Mille Lacs and Kanabec Counties. Virtually all of the damage was minimal due to the rural location. I don't believe
there were any injuries reported. The rain free base appears to be pretty small here surrounded on at three sides
by rain. The hook itself is quite large suggesting a developing HP supercell. We shall see in the following radar
loop, that that is just what happens.
Here is the velocity image for the same cell at the same time. The couplet is highlighted by the red circle. Notice
the radar return suggests that at one point, there is a 40 knot wind towards the radar system very close to a 50 knot
wind away from the system. This condition is near the center of the circle. This suggests intense rotation and represents
the F3 tornado that is on the ground. Remember however, radar only detects mid-level rotation in the mesocyclone. Low
lever rotation can only be seen by spotters in the form of a wall or funnel cloud or tornado. NEXRAD does a great job
of detecting the possibility of many tornados. But it cannot confirm a tornado, nor can it see most of the more weak,
lower level versions usually found in LEWPs and bow echoes.
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