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Using Doppler Radar to Protect Life and Property Most people are familiar with the "reflectivity" data (see picture bottom left) which the radar produces. This data is the colorful picture most people see on TV and on the internet that shows where the storms are and how strong they are. Another useful product the radar produces is the "velocity" or Doppler data (see picture bottom right) which shows which way the winds are blowing in the atmosphere. Areas that are colored red indicate winds that are blowing away from our radar site. Areas that are colored in green indicate winds that are blowing toward the radar site. The radar site in the pictures below is located to the southeast of these images. The brighter the color, the faster the wind is moving. Click here for a more detailed explanation of how the Doppler radar works.
The Doppler radar is a key tool in discerning which storms are capable of producing a tornado. Click here to see a radar reflectivity loop of a tornadic thunderstorm that moved through Fort Worth, Texas. Then, click here to see the radar velocity loop of the same storm. Can you pick out the tornado signature? |
When the weather takes a turn for the worse, we need to gather data quickly. The National Weather Service has a 
In general, when we see bright red colors right next to bright green colors on the velocity image in the same location that the reflectivity image is showing a severe thunderstorm, we can infer that the winds inside the storm are rotating. To demonstrate, hold a pencil between the palms of your hands and move one hand away from you and one hand toward you. The pencil begins to rotate. The pictures below show what a tornado looks like on radar. See how different the storm looks on the reflectivity picture as compared to the velocity picture. As you can see, not all severe storms rotate.
