I have always looked up to the heavens to wonder what is happening when clouds are formed, why the sky is sunny, what is wind, and all the other meteorological phenomena, but, especially tornadoes. It’s amazing to realize that tornadoes are only a very organized movement of air. Scientists are not sure how the actual tornado forms, but there are certain things that must be there to form a tornado.

We need to start by looking at a thunderstorm before we can get to a tornado. Let’s look at a simple thunderstorm to help understand the anatomy of a storm. A storm needs unstable air, or conditionally unstable air. This warm, humid air as it rises starts to cool until it reaches it dew point. A cloud starts to appear. The updraft continues upward, creating a cumulus cloud. In the tops of these clouds, ice crystals and super-cooled water drops initiate the Bergeron Process, and they grow until they’re big enough to overcome the strength of the updraft. As rain falls, it evaporates in a very dry air entrained into sides of the cloud. cooling the air. This cooler air sinks, causing downdrafts. Updrafts continue to feed the storm, as downdrafts start to choke off the updraft, eventual killing the storm (Williams, 118).

A supercell thunderstorm is the king of storms. It’s a massive system, a very organized wind machine with very strong updrafts and downdrafts, tornadoes, and hail. It is able to keep itself going for several hours, travel over 300 miles, and can spawn the most dangerous tornadoes (Williams,124). Before we explore how supercells live and die and create tornadoes, there are some essentials to get this storm going. The first item needed is unstable air. Unstable air is air that wants to rise either because of heating, or because it’s forced up from a cold front or mountain side. To make a thunderstorm, it needs massive updrafts to create the cumulonimbus clouds. The second requirement needed is an upper-air disturbance (Williams, 120). The upper troposphere is made up of troughs and ridges, called long waves. Sometimes a ripple, or a short wave, will appear in these long waves. A storm will show up on the east side of a short wave (Williams, 57). This short wave causes an upper air disturbance, because the air aloft is diverging, creating a surface low (Williams, 60). Hence, air converges at the surface becoming unstable. The third item is an inversion layer of stable air (located at approximately 800 mb) on top warm, humid air, with an unstable environmental lapse rate above the inversion (Ahrens, 418). Without the inversion layer, only pretty, fluffy fair weather clouds will appear. As the surface air is heated or is pushed up, pressure builds up underneath the inversion layer. Then, like a boiling pot with a lid on it, the pressure becomes too great, and BLAM!, the air explodes through the layer of stable air into the unstable air above the inversion. The updraft can shoot up to 50,000 feet or more, sometimes in just minutes, moving at 150 mph (Davies-Jones, 3). The fourth item needed is wind speeds that increase with altitude (Williams, 120). Fast moving air aloft interacts with the updraft, promoting rotation in the system and keeping the storm going. The upper level winds cause the thunderstorm to tilt, essential to the life of the storm. Because of the tilt, the sinking air is not forced down interfering with the updraft. If this were to happen, the storm would be choked off and die (Williams, 127). The fifth requirement is that the storm must have a fresh supply of humid air that is continuously feeding the storm (Williams, 120).

If all the requirements are met, a series of events must happen. As mentioned before, the storm needs unstable air. As the air begins to rise, a mesocyclone starts to form. A mesocyclone is a vertical rotating column of air in a supercell. It is the key to its long life and power. It organizes the flow of cool, dry entrained air from above and warm, humid air from below. The mesocyclone is born as slow, south winds close to the ground and fast, westerly winds aloft start a tube of air to spin horizontally. Faster and faster the tube of air spins until updrafts from the pending storm lift the tube of air so it turns vertically (Williams, 125). This vertical column of air is the mesocyclone. The mesocyclone generally spins in a counter-clockwise motion, moving more than 50 mph, and is about one to three miles in radius (Davies-Jones, 4). It is the shaft were the main updraft will occur. The supercell’s life is dependent on this column of rotating air (Williams, 127). It keeps it all organized. Also, this is were the tornado will occur if the system is ripe for one.

As mentioned, air must be coming in at different directions, and at different speeds to keep the mesocyclone going (WW2010). Let us identify the three major altitude regions of wind as mid-altitude, upper level, and surface.

Mid-altitude winds come into the storm from the rear (or on the west or southwest side). As this dry, cool air enters the system, rain evaporates, cooling it even more. The cooling air becomes cooler than the surrounding air, sinks, and forms a strong downdraft. Part of the downdraft goes out of the system in the direction which it came (This called a rear flank downdraft) (Williams, 125). Some of it gets caught by the spiraling winds of the mesocyclone, and is pushed towards the front of the storm at ground level. This is called a gust front. Most of us have felt the effects of a gust front by the dropping of the temperature before it rains. Finally, some of downdraft air becomes part of the mesocyclone once more.

Upper level winds, coming from the west southwest, help give the supercell its tilt and anvil shape. Some of these winds create a downdraft in the front of the storm called the front flank downdraft (Williams, 125). As the storm moves, the gust front and the front flank downdraft acts as a plow forcing a fresh supply of air up into the mesocyclone (Williams, 125).

Surface winds usually come from the south southeast into the storm. Warm, humid air is sucked into the system, providing fuel to keep instability going. As more air comes in, releasing latent heat, huge amounts of energy are released to power the storm.

The requirement for the different wind speeds and direction is the necessity to push the downdraft and rain away from the updraft summit. If the updraft and downdraft share the same summit, the downdrafts would choke the updraft, hence losing its power supply (WW2010).

With all this updraft and inflow, air does not just sit there piling up. The storm must have an exhaust system. Outflow is just as important as the inflow. As I mentioned before, one of the outflows is the gust front. The gust front is the boundary between the warm, humid air and a cold downdraft (WW2010). As mentioned before, we sometimes feel it right before it rains. This boundary is very important. Rear flank downdrafts and front flank downdrafts are all important to keep the storm alive.

Picture from WW2010 CD-ROM

All this outflow creates a boundary around the storm (shown in blue). Of most importance is the boundary in front of the storm, the gust front. Remember, the mesocyclone is the main updraft of a storm (shown in picture above). The cold air of the gust front gets wrapped up in the circulation, and causes a bend in the gust front (this wave is shown as an indentation in the blue line in the Main Updraft). This bend in the outflow boundary allows warm, humid air to be pulled in the system without becoming undercut. As the storm moves, the outflow grows stronger and stronger, and the boundary bends out from the main updraft. This is the undercutting of the storm which eventually chokes the storm. This main updraft (the mesocyclone) is where the tornado will spring into existence.

The wall cloud is an interesting part of meteorology. It isn’t part of the tornado, but an extension of the mesocyclone. It is created from downdraft that get sucked in the mesocyclone. "The cool air has higher relative humidity than the warm air and if forced upward becomes cloudy at lesser heights. Thus, when some of this air is sucked into the updraft, a lowered wall cloud forms" (Davies-Jones, 4). If you see this wall cloud rotating, BEWARE!!! It could be brewing a tornado as you watch it.

This is where the science becomes iffy. The coriolis effect is not of significance, because some tornadoes in the northern hemisphere have been photographed spinning clockwise (looking down at it) (Williams, 129). Scientists have also seen the evidence of tornadoes starting from the ground up, and also, starting from the mesocyclone down. Two main theories of tornado genesis exist today.

One is similar to the mesocyclone development. A small horizontal eddy forms below the clouds. A downdraft cuts the eddy in two, one clockwise, one counterclockwise, and turns them vertical. The counterclockwise half is stretched by the updraft connecting the newly formed column of air with the mesocyclone, hence a tornado is formed (Williams, 129). (The other half spins slower and slower as it circles the larger one, until it runs out of energy) (Williams, 129).

The second works the same way an ice skater can spin faster and faster. As winds fly into the mesocyclone, the rotation rate increases by conservation of angular momentum. This causes the mesocyclone to stretch vertically, and shrink horizontally. As the winds flowing into the system increase, it gradually extends down to the ground.

As the tornado moves along its northeast track, the rear flank downdraft (blue arrows) pushes the gust front (bottom blue line) forward. The inflow has plenty of room to rise in the mesocyclone and the wall cloud (the center of the picture).

Figure # 1

‘T’ is tornado, red arrow is inflow, blue line is outflow

Picture from WW2010 CD-ROM

Figure # 2

‘T’ is tornado, red arrow is inflow, blue line is outflow

Picture from WW2010 CD-ROM

Figure # 2 shows the gust front closing in on the wall cloud and the inflow. The question mark indicates another wall cloud that could be forming east or southeast from the original tornado (WW2010). Sometimes, it’s missed when the existing tornado has center stage. The rotating rain around the mesocyclone is pick up on Doppler radar as a hook echo (Ahrens, 422). This tells meteorologists some sort of rotation is happening within the supercell, usually a tornado.

Figure # 3

‘T’ is tornado, red arrow is inflow, blue line is outflow

Picture from WW2010 CD-ROM

Eventually, the gust front squeezes out the original wall cloud, choking the updraft. At this point, the downdrafts start to tilt the tornado horizontally as the funnel fades into the dissipation stage. It forms into a ‘rope’ look, till it eventually disappears. As mention before, and as shown in this diagram, a new wall cloud has sprung up, and starts its own life.

Picture from WW2010 CD-ROM

This photo above shows how the outflow and inflow works in the real world. The black line (Leading Edge Of Outflow) is the blue line in figures #1-3 show above. The inflow in this picture is strong, and is able to keep the storm alive.

Picture from WW2010 CD-ROM

The next picture shows the Leading Edge Of Outflow is farther out, and the outflow is beginning to undercut the inflow. The old wall cloud starts to fade, but a new wall cloud begins to show.

Wind is the major problem with tornadoes (compared to storm surges with hurricanes). Winds can reach as fast as 300 mph. But, normally reach up to 150 mph. At these speeds, railroad cars can be tossed like Hot Wheels. As air spirals toward the tornado, it gains speed picking up anything in its way. Most tornado deaths happen when pieces of building get caught in the wind, and are whipped like missiles (Williams, 123).

Unless water vapor condenses to make the twister visible, tornadoes are not seen until the dirt is sucked into the vortex (Williams, 123).

Each tornado has a vortex which is the suction of the tornado. Most tornadoes are multi-vortex. Scientists are trying to prove that multi-vortex tornadoes are created by air sinking into a single vortex tornado, causing a breakdown of the vortex. Each vortex becomes a ‘vacuum cleaner’, making the twister more powerful then ever. This phenomenon has been proven in the laboratory, but it is a little tough to prove in nature, considering everything is destroyed as the twister rolls over.

Tornadoes occur at different times of the year, and at different places. Here in Florida, tornadoes tend to hit in January, February, and March. Tornadoes can hit anytime of the year, or anyplace, it just needs warm, humid air below an inversion layer to create build-up of the system (Williams, 123).

Thunderstorms and tornadoes are an awesome display of power that nature can offer. But, we must respect the storm. It is a deadly force. After seeing what the tornado did to our town, I hope people are smart when it comes to these storms, and not test fate. Tornadoes are cool, but so is living.