Tuesday, October 22, 2019

Supercell "Right Turns" -- A Tornado Warning Tipoff

For those that follow tornado meteorology closely here is some information about informing yourself via radar which supercell thunderstorms tend to produce tornadoes.

One of the things we look for is a supercell thunderstorm that makes a "right turn" relative to both the other storms in the area and its original path. Using Sunday's Dallas thunderstorm as an example, here are some illustrations.
Things were starting to become clear at 7:26pm Sunday evening as the northern storm was moving (relatively) rapidly northeast while the storm to its south was slowing. The "left-mover" (the northern storm) typically produces large hail while a right turning southern storm is more likely the tornado producer.
A half-hour later, at 7:58, the northern storms moved rapidly to Valley View while the southern storm over Tarrant County has slowed down and begun its right turn).

About fifteen minutes later the northern storm is getting ready to cross into Oklahoma while the southern storm has completed its right turn. At this point, I was tweeting for people in its path to be ready to take shelter "at a moment's notice."

Here is a closeup of the right turn.
There is more to tornado warnings than right turns. For major tornadoes, we look for,
  • Hook echoes. 
  • Velocity couplets (showing rapid rotation)
  • Sometimes positive polarity lightning 
  • Debris signatures 
It takes a lot of training and experience to get good at tornado warnings. However, if you are watching a supercell thunderstorm in a tornado watch, a right turn is a good indication that the situation may be about to get more dangerous.

The knowledge accumulated the last 50 years has led to America's amazing storm warning system that has saved tens of thousands of lives. That warning system worked well Sunday. As one reader put it while Sunday evening's storm were still in progress:

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