With a basic understanding of thunderstorms under our belts, we can take a look at their perhaps most recognized, feared, and damaging progeny – Tornadoes. Though the vast majority of storms never produce one of these phenomena, the United States sees more tornadoes per year than any other country on earth. Every US State has observed a tornado at least once, with Texas reporting, by far, the most (on average) per year. There are countless myths and misunderstandings about tornadoes and, truth be told, their development (like many other weather phenomena) is still not completely understood. The following explanation reflects the most agreed upon understanding of how these weather powerhouses develop.

As we recall from the last entry, thunderstorms are composed of a series of strong updrafts and downdrafts, working in concord to produce gusty winds, heavy rains, lightning, and sometimes hail. In the most severe of thunderstorms, (known as “supercells”) this symbiotic cycle of winds can eventually lead to the formation of a “mesocyclone”, resembling a horizontal rotating tube. Meanwhile, if this kind of storm development is taking place, one can expect the rain falling from the super-high cloud (sometimes reaching upwards of 60,000 feet!) to be incredibly heavy and tending to fall toward the rear of the storms movement.

The weight of all that falling rain creates a massive downward force on the back end of the mesocyclone, leading the once horizontal rotation to begin tilting vertically. This “downward force” is known as the Rear Flank Downdraft (RFD) and since it brings down colder air and moisture from higher heights, water tends to condense around the mesocyclone, forming what’s known as a wall cloud. (Tornado chasers look for this wall cloud since, once observed, the chance of a tornado forming is much greater) As the mesocyclone continues to tilt more and more vertically, the lower end begins to tighten up and become more concentrated, leading to the updraft inside being squeezed through a smaller entrance. This, in turn, speeds up the mesocyclone and the funnel cloud is born. The strongest mesocyclones will have their funnel cloud reach the ground and a tornado is born.

The properties of tornadoes can vary widely, as a myriad of factors are at play. The width of a tornado can range from just a few feet to over a mile or two, while the lifespan of one of these behemoths varies between a few seconds to over an hour! Though it is true that wide open spaces (like the Central Plains of the USA) are most conducive to tornado development, cities are not immune from the risk and even New York City sees a twister from time to time. The longer a tornado lasts on the ground, the more damage it will do and some twisters have been known to travel hundreds of miles before dissipation.

Speaking of dissipation, the major factor in producing a tornado is often the same as what leads to its demise. As the RFD tilts the mesocyclone down to the surface (creating the tornado), it tends to slowly encapsulate the circulation. Though this process can take some time, once it completely engulfs the tornado, the necessary inflow of air is cut off and the storm will eventually die. The pace with which this happens is often dictated by the groundspeed of the storm, its intensity, or the storm’s ability to regenerate new mesocyclones that can produce replacement tornadoes. Regardless, as soon as the funnel is gone, the winds (blowing sometimes over 200mph) die down almost instantly and all that’s left is the debris in the air and the damage on the ground.

Understanding how we detect these storms is almost more important than how they work. Nowadays, most meteorologists around the world have Doppler radar to utilize in finding likely locations of tornadoes. The radar is able to detect the direction of winds within a given storm. When winds blowing rapidly in opposite directions are detected next to each other (indicating rotation), this is often thought of as a very likely spot for a tornado to be. (“Tornado Signature”) Within moments of this observation, Tornado Watches/Warnings are issued and people in the vicinity are ordered to seek shelter immediately.

The aviation industry knows full well how dangerous and life threatening a tornado can be. Cloud tops, as mentioned earlier, can exceed 60,000 feet in one’s vicinity and extreme winds, hail and lightning can do fatal damage to aircraft nearby. In many ways, a tornado poses more of a threat to aircraft on the ground, since unlike airborne planes, those sitting at the gate cannot “change their route.” In June, Denver International Airport was ordered shut down for 40 min, leaving passengers and employees scrambling to take cover when a Tornado Warning was issued. Wind gusts of near 100mph were observed on the field before communication with weather instruments was severed. Though no damage or injury was reported, the situation could have gone very differently with 1000s of lives and billions of dollars worth of aircraft and equipment at risk.

Adam Daum is a Senior Aviation Meteorologist with WSI and is embedded within the System Operations Center of a major NY-based airline. Hailing from Oceanside, NY, Adam graduated from Cornell University in 2005 and spent the next 5 years working at NBC News’ “The Today Show” and NY1 News as a weather producer. His love for Aviation (and Israel) led him to join the Israeli Air Force in 2010 and work as an Aviation Forecaster for the Israel Meteorological Service from 2011-2013.