Supercell spawns extremely rare ‘clockwise’ tornado in Oklahoma
Almost all tornadoes that develop in the Northern Hemisphere will have winds that spin counterclockwise—or cyclonically—and follow a typical northeastward track. But sometimes these dangerous storms can throw meteorologists a wicked curveball, deviating from the norm and leaving experts scrambling.
Two such instances happened on April 30, when a supercell southwest of Oklahoma City produced a tornado whose track looped around on itself, and then spawned an anticyclonic tornado with winds spinning clockwise.
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While it’s unusual for a tornado’s track to loop back on itself, it has happened several times in recent history. The most famous instance of this happening is the 2013 El Reno tornado, which gained infamy when it unexpectedly grew and looped around on its track twice. This tornado tragically claimed eight lives, including four storm chasers who were caught by the tornado’s sudden and erratic behaviour.
“The motion of a tornado is closely tied to the motion of its parent storm. If the parent storm is moving quickly along a linear path, then the tornado likely will follow along,” states Michael Carter, a meteorologist for The Weather Network. “But if the parent storm is slow-moving or even stationary, the tornado’s path might meander or even loop back on itself.”
This is likely what happened on April 30. The National Weather Service in Norman, Okla., stated in their tornado warning for the second anticyclonic tornado that it was “nearly stationary or moving very slowly south,” which means the parent supercell to these tornadoes was also likely very slow moving.
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Luckily, the tornadoes on April 30 stayed over open farmland, resulting in no casualties.
What is even more rare than a tornado doubling back, however, is an anticyclonic tornado. Only 1 per cent of tornadoes that form in the Northern Hemisphere ever spin clockwise, making the April 30 tornado an extremely rare occurrence.
“Under certain conditions, strong thunderstorms can split into a pair of supercells, each rotating in opposite directions—clockwise and counterclockwise. In the northern hemisphere, the atmosphere tends to favour counterclockwise, or ‘cyclonic’ rotation,” Carter says. “So typically, the cyclonic supercell thrives and strengthens. Meanwhile, the cell rotating clockwise, the ‘anticyclonic’ cell, weakens and dies.”
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“However, sometimes the anticyclonic cell does survive long enough to strengthen and produce a tornado. This tornado, like its parent storm, will also be anticyclonic.”
When an anticyclonic tornado does spawn, it is usually smaller and fairly weak. That being said, anticyclonic tornadoes are still something that should never be taken lightly; they’re just as incredibly dangerous as their cyclonic counterparts.
Tornadoes are a common occurrence in the southern United States and the Midwest, with almost 70 per cent of the country’s yearly tornadoes occurring between March and June there. Warm, moist air from the Gulf of Mexico meets the jet stream to create a perfect blend of ingredients over the region for tornadoes to form.
Contains files from livescience.com.
Thumbnail image of a tornado in Alberta, taken August 3rd, 2020, courtesy of Kyle Brittain.