How to Identify Possible Tornado-Producing Storms on Doppler Radar

Learn how to spot tornadoes on Doppler radar.

Tornadoes can be terrifying, and glancing at the Doppler radar screen on television can be confusing. Knowing what the meteorologist is referring to when he shows you the Doppler radar screen can help you understand when a tornado is likely to occur. By learning about the pixel patterns on Doppler radar screen, you can decipher the greens, reds and yellows as they relate to tornado-causing storms.

Instructions

1. 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.

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.

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.

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.

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.

6. Check for a kidney bean-shaped supercell. Storms of this shape tend to produce tornadoes.

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.

References

• San Francisco State University Geosciences: Hook Echo
• The Storm Track: Detecting Tornadoes on Radar
• Cooperative Institute for Meteorological Satellite Studies: Doppler Radar