1999 Oklahoma tornado outbreak. It reached F5 strength on the Fujita scale.]
Kansas City, Missouri.] The hook echo is one of the classical hallmarks of tornado-producing supercell thunderstormsas seen on weather radar. The echo is produced by rain, hail, or even debris being wrapped around the supercell. The National Weather Serviceconsiders the presence of a hook echo as sufficient to justify issuing a tornado warning.
The hook echo has been recognized as a sign of tornado development for most of weather radar's existence. The first documented tracking of a hook echo was on
April 9, 1953by the Illinois State Water Survey, during preparations for an early test of radar's ability to measure rainfall rates.
Hook echoes are not always obvious. In the
U.S. Southern states, thunderstorms tend to produce heavier rainfall which leads to the high precipitation (HP) variation supercell and obscures the hook shape. HP supercells will instead take on a kidney bean shape.
The use of doppler radar systems such as
NEXRADallows for detection of tornadoes even when the hook echo is not present, and for greater certainty when it is. By detecting the relative velocities of different parts of a storm, doppler radar can detect areas of rotation.
Bounded weak echo region
Tornado vortex signature
Convective storm detection
* [http://chill.colostate.edu/w/CHILL_history The First Tornadic Hook Echo Weather Radar Observations]
* [http://www.srh.noaa.gov/meg/presentations/radar/sld026.html National Weather Service presentation on Radar Interpretation] - slide 26, detailing the difficulties of spotting hook echoes in the south
* [http://www.crh.noaa.gov/unr/?n=07-10-00 July 10th, 2000 Severe Weather (NWS)] - includes discussion of tornadic radar signatures
* [http://www.wdtb.noaa.gov/modules/twg02/TWG2002.pdf NWS - Tornado Warning Guidance: Spring 2002] (72kb PDF)
* [http://www.wdtb.noaa.gov/modules/sls00/M3RADAR.pdf NWS - Analysis of May 3, 1999 Oklahoma City Tornado Signature]
* [http://amsglossary.allenpress.com/glossary/search?id=hook-echo1 Hook Echo] - AMS Glossary of Meteorology
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