Hook Echoes
The first thing one needs to know is that precip echoes are just that, they are precip echoes.
Falling rain, hail, debris and or things in the way such as wind turbines, bats, birds is reflected by the radar. The current radar network made up of WSR 88 Ds, 88 standing for 1988 the year they were brought into service. Are the best we have in the weather community. Although they are being upgraded as we speak to Dual pole. That is not important right now.
Radar or pulsed Doppler radar is a system that sends out beams that bounce off rain and large cloud material to send back information on size and density of the cloud droplets.
Hook Echoes were first recognized by the early 50s when weather radar was in its infancy. It was then very noticeable that these tornado producing thunderstorms seemed to display a common characteristic.
The hook echo itself is actually a display of rain and or hail being wrapped around the updraft cyclonically due to strong updraft winds. The hook echo isnt a tell tale sign there is a tornado but more of a sign your dealing with a supercell. Or rotating updraft. Not all supercells have hook echoes and not all hook echoes mean a tornado is present. But it is a strong indication that one is either possible or already on the ground. The variances are still not well understood!
Below is an instructional webpage showing a hook echo and many other supercell related features.
http://www.spc.noaa.gov/faq/tornado/radscel.htm
Below are examples of hook echoes.
The image above shows 4 supercells with hook echoes. The ones to the south are actually so close its hard to point out the hooks but they are their. The two cells to the north are easier to pin point. With one having a classic hook signature and the other being more HPish in nature.
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