24 Jun Have You Ever Seen A Thunderstorm Spin?

Have you ever heard the term a “rotating” supercell thunderstorm?

All tornadic supercells will rotate, but not all rotating supercells produce tornadoes.   Just by looking at a rotating supercell thunderstorm, you can tell it’s different than the normal thunderstorms you see in the summer.   You know, those that offer a brief respite of rain over your parched lawn, then quickly dies out and the brutal summer sun once again bakes everything into a crisp golden brown?   A rotating supercell, just by it’s appearance, will look like it has a “swirl”.  Watch it over a period of time and you can tell it’s contorted a bit and seems to rotate a bit.  However, if you watch a timelapse of it, you will see why they’re called “rotating” supercells.

I took this video near Dublin, Texas on April 26, 2015 of a rotating supercell.  It was Tornado Warned and did produce a couple of rain wrapped tornadoes.  In the video you can see it spinning like a top.  This storm begins as warm air rises in the spring time sun.  As it rises, it begins to encounter different wind speeds and directions at different altitudes.  We call this wind shear.  It may be a southeast wind at 20mph at the surface, a southerly wind at 40mph at about 2,500 feet and maybe a southwest wind at 55mph at 5,000 feet.  As the warm air rises quickly, it stays warmer than the air it surrounds, causing it to condense into clouds and continues to rise.  It will begin to twist and turn at the different altitudes because of the wind shear.  The storm then begins to feed off of itself and rotate more and more, faster and faster, sometimes forming a tornado at the surface.

They’re called supercells because they are not your normal thunderstorm.  They are isolated and pretty much control the surrounding environment.  They can sustain themselves for a much longer period of time than a normal thunderstorm because the rain or downdraft portion of the storm stays separate from the updraft (or engine).  As long as the updraft can sustain itself, the storm will continue to march on.

But all this turning and rising starts with a few molecules of warm air rising.

Next spring, watch those isolated supercells and see if you can notice the spin.

– Mike Prendergast

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