A large “wedge” tornado struck Tupelo, Miss. on Monday afternoon. The tornado was spotted from a towercam from WTVA-TV before the internet stream I was watching failed.
This image from the computer program GR2Analyst was tweeted to me by @WxChaser_:
The column of “cool colors” depicts debris lofted four miles high from the Tupelo tornado. (@WxChaser_)
It’s a truly astounding image and is relatively new in Doppler radar technology. This isn’t a traditional radar image depicting rainfall or even wind within a storm. We’ve had that for years.
But in this fairly-new dual-polarization radar product — called correlation coefficient — the radar determines whether the objects being detected by each radar pulse are “similar” in general shape or orientation to the other objects seen by other pulses tiny fractions of a second apart.
The warm colors indicate rain, hail or snow in the cloud– there’s not much change in their shape or orientation between radar pulses. And that’s what you’d typically find in a thunderstorm.
However, in that column of cool colors, the objects — as meteorologists put it — are not “well-correlated.”
In plainspeak, within that column that stretches more than 20,000 feet into the atmosphere, the radar is telling us that it’s seeing objects of all shapes and sizes.
Things of different shapes and sizes are not supposed to be four miles up in a thunderstorm.
That can only mean one thing — debris from the earth has been lofted by the tornado miles into the atmosphere. Truly terrifying.
That’s the tornado debris signature and actually an indication of the shape and size of the tornado itself.
In fact, the tornado column and the parent supercell thunderstorm are “tilted” in response to increasing upper-level winds the higher you go into the sky.
Now, we don’t have to “slice” the storm to get a view of a tornado debris signature.
This is how the correlation coefficient product looked about the same time. You can clearly see the spot of blue — the area where the radar is detecting debris, and thus, the tornado itself.
The so-called “debris ball.”
An area of poorly-correlated radar echoes associated with the Tupelo tornado.