Learning About Weather Radar ... The Debris Ball
On March 2, a lot of people heard me on TV immediately identify something on radar and refer to it as a debris ball. From this point forward on March 2nd, I referred to this tornado as "strong to violent" and spoke of the situation as a "life threatening situation". In this blog, I want to teach you a little about how a radar works and what a debris ball really means.
How Does A Radar Actually Work???
The NWS has a good and short video that explains a little about how radar works...
Basically the radar sends out a beam of energy we can the pulse of energy. As this pulse of energy goes past things like rain or hail, it can "reflect" some of that energy back to the radar. If the object is large or there are lots of objects to reflect the energy, then you start to get more and more energy sent back to the radar. We call this reflectivity. As you know, dark colors like red or black = bad! Those colors mean lots of energy is being reflected back to the radar from things like hail or tons of heavy rain. Since the radar can see anything (even non weather items), then we can get "bright" spots sometimes on radar when we are tracking tornadoes. The bright spots can sometimes indicate tornado touchdowns if they appear on the correct part of the storm and when this happens, we call it a debris ball.
What Is A Debris Ball?
Now that you know a little more about how a radar works, we can talk a little more about what "debris ball" is. A debris ball is a radar signature that "implies" that tornado has destroyed something and is lofting the debris in the air. Well you already know that reds and blacks on radar mean the radar is seeing a lot of rain, hail, or if it is where a tornado should form on radar then it can mean debris. If you have watched me during severe weather, then you know the "hook" on a thunderstorm is where the tornado will form (southwest edge of the storm). Since a tornado has the ability to pick up some big things, sometimes we get debris balls that can be very strong indications of tornadoes. Some research has shown that debris balls can verify tornadoes on the ground accurately up to around 70% - 80% of the time. Let's now look back at March 2nd and I will show you more...
Examples Of Debris Balls
Let's start to look at how storms look on radar and how to identify a debris ball. The image below is the supercell that tragically did so much damage in our area on March 2nd. You can see the body of the storm and the hook on the southwest side of the storm. The hook appears because the storm is rotating so fast that it pulls rain around the dry side of the storm and wraps it around the rotating updraft (where the tornado could form). Legit hooks only show up on rotating storms.
In the above image, there is no bright colors in the hook, so there is no debris ball. Keep in mind, we are simply trying to identify if a debris ball is present. As the storm moved through Pekin, I was watching extremely closely to see if a debris ball would form knowing that it would indicate a very high likelihood of a strong to violent tornado. You can see the purples show up in the center of the hook right as the storms moved through Pekin, IN. This is a debris ball showing up on radar.
Here is a close-up of the same very obvious debris ball.
From this point forward, the southern IN supercell had a noticeable debris ball for the better part of 50 minutes. As it left Henryville, IN the debris ball intensified on the storm as it had clearly did extensive damage in the city.
Does A Debris Ball Occur On Every Strong / Violent Tornado?
Remember a debris ball is the tornado lofting the things it destroys up into the air. The radar is simply "seeing" the high reflectivity debris spinning around near the tornado. This means debris balls will show up normally as strong to violent tornadoes hit populated areas. I archive all tornado events in the US to study how every event looks on radar, so I can go through the images one by one to make sure I am radar ready when you need me. Let me show you some of the cases over the last year that show very obvious debris ball signatures.
Finally here is the MASSIVE debris ball from the May 20, 2013 Moore, OK EF-5 Tornado. Notice how intense this debris ball was!!!
Understanding The Debris Ball
My history and background before I got into television was research. I am a grad student who worked under an incredibly well known radar meteorologists named Josh Wurman. The name may be familiar because Josh Wurman is the inventor of the Doppler On Wheels.
I was involved in research projects studying numerous hurricanes, microbursts and downdrafts, and many of the tornado studies in the late 90s. My expertise is in radar meteorology. I think I find radars so interesting because they can see where our eyes cannot. They can see into clouds, rain, hail, and even into tornadoes. Understanding how radars work and what they are indicating has been the greatest fascination I have had as an adult. There are so many more things a radar can see than what I have shown you tonight, but since the weather is quiet, I wanted to teach you a little about how radars work and how they can indicate tornadoes. Next time you look at the radar, I hope you do it with a little more understanding of what you are looking at and if you ever see a debris ball on radar then you will know know how dangerous the situation is.
If you ever have any question, please remember I can be reached on facebook or twitter easily! Just follow the link below to my facebook or twitter page and click "LIKE/FOLLOW"!