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The city of New Orleans, Louisiana made weather news headlines in 2017, not because of a coastal Atlantic hurricane, but because of the New Orleans East tornado, rated an EF2, that touched down in early February of that year. It left many wondering how such a large and strong storm could occur so early in the tornado season, and asking, What is a wedge tornado?
A "wedge tornado" is what storm spotters name a tornado that takes the shape of a wedge or an upside-down triangle. Unlike funnel-shaped tornadoes, the wedge tornado has straight sides and looks as wide, or wider, than it is tall.
Large, But Often Hidden in Plain Sight
Due to the broadness of wedge tornadoes, they are thought of as the largest and most menacing of tornado types. Its size is so broad, in fact, that at first glance it's not recognized as being a tornado. A wedge tornado's base (the part of the storm that touches the ground) can be a mile or more wide and often look like low-hanging dark clouds to passersby. That's why these "fat" storms are often the tornadoes survivors blame the most for "striking without warning."
As if they weren't already difficult to see, wedges can also be "rain-wrapped." When this occurs, curtains of nearby rainfall encircle the tornado funnel, making it that much more veiled from view.
Why So Monstrous?
Thankfully, wedge tornadoes make up only a fraction of tornadoes. Roughly 2-3% of confirmed tornadoes from 1950-2015 have been wedge-shaped. (Source: "Two Reasons We Have to Stop Throwing Around the Term Wedge Tornado" Washington Post, April 2016.)
Like ordinary-shaped tornadoes, these mile-wide monsters form when warm, moist unstable air collides with dry, stable air in a region of enhanced lift and strong vertical wind shear. The secret to their mammoth size is still somewhat unknown, but it's believed the formation of multiple vortices around the main funnel helps to expand the width of the storm's total wind field.
Wedges are more common in the southeastern U.S., which is located next door to the moisture-rich Gulf of Mexico. Clouds in this region also tend to hang at low levels in the sky, which means should a tornado form, its funnel will likely be short and stout (a requisite of a developing wedge tornado).
Wedge Width is NOT a Measure of Strength
Given their apocalyptic appearance, there's a misconception that wedge tornadoes will always be powerful tornadoes, but this isn't necessarily true. There have been wedges that were rated as weak EF1 tornadoes, so clearly a tornado's size has nothing to do with its strength.
However, it is true that wide tornadoes have a tendency to also be quite violent. At 2.6 miles wide, the May 2013 EF3 El Reno, Oklahoma wedge tornado is proof of this. It holds the record as the widest tornado ever measured on Earth. A number of the most violent U.S. tornadoes have, in fact, been wedges. These include the May 2007 Greensburg, Kansas; 2011 Joplin, Missouri; and the 2013 Moore, Oklahoma tornado disasters.
Other Tornado Shapes to Look For
Wedges are just one of a number of shapes tornadoes can take on.
A "stovepipe" tornado has a long, cylindrical shape and is named for its resemblance to a roof or chimney stove pipe. "Rope" tornadoes resemble strings or ropes because of the curls and twists in their long, skinny funnels. They can describe narrow tornadoes or signal a dissipating tornado, since as the funnel lengthens the winds within it are forced to weaken (due to conservation of momentum) and its circulation to shrink-a process called "roping out."
Of course, the classic twister bears a cone shape, with the storm at its widest where it meets the clouds and a tapered base at ground level.