How to Identify Possible Tornado-Producing Storms on Doppler Radar
Instructions
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Scan Doppler radar for a "hook echo." The term refers to a hook shape on the screen that occurs when rain, hail and debris are rotating around a supercell or thunderstorm. The National Weather Service considers the presence of a hook echo on Doppler radar sufficient grounds for issuing a tornado warning.
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2
Check the velocity pattern on the Doppler screen for a tornado vortex signature, or TVS. A TVS indicates there is an intense rotation taking place inside a supercell, enough to indicate that a possible mesocyclone, or continuously rotating updraft of air, is occurring. This mesocyclone can become a tornado.
The TVS will be represented by a green pixilated area next to a red pixilated area on the Doppler radar. This image indicates competing wind strengths and is a sign that a funnel cloud is in the area.
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3
Scrutinize Doppler radar for an area of the storm where rain should be occurring but is not because of a strong updraft pulling the precipitation in another direction. This is known as a weak echo region, or WER. On the radar screen, it is an area of green or yellow pixels encased by dark red or orange pixels.
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4
Look for a rear flank downdraft, or RFD. When dry air circles around the back of a mesocyclone in a thunderstorm, an RFD occurs. The descending air is needed to produce a tornado. On the Doppler screen, it appears as a red, pixilated wave. Beneath it is a triangle of green or blue pixels known as the inflow.
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5
Study Doppler radar for reflectivity, which is the intensity and movement of precipitation. This will appear as a fan shape near the inflow area.
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6
Check for a kidney bean-shaped supercell. Storms of this shape tend to produce tornadoes.
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7
Inspect radar images for a bow echo, so named because it is shaped like an archer's bow. It appears as a red, sideways hump in a field of green pixels. The bow echo occurs when focused, strong winds exist in the lower atmosphere, causing violent wind gusts and property damage. A bow echo is a sign that tornadoes are present.
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