The massive tornado that struck Moore, Oklahoma, on Monday was the fourth significant tornado to hit that city during the past 14 years, each during the month of May
Moore, a city of some 55,000 people, is a suburb of Oklahoma City, which lies directly in the bull’s eye of what is referred to as Tornado Alley, the area of the country most prone to producing tornadoes. Historically, Oklahoma City has had more tornado strikes than any other city in the United States, and many of those strikes have been large and deadly. Within the past 14 years, Moore has been struck four times, each time during the month of May: May 3, 1999, May 8, 2003, May 10, 2010, and May 20, 2013.
Monday’s tornado was massive, measuring more than a mile wide, and was initially given a preliminary rating of EF-4 on the Enhanced Fujita Scale. On Tuesday, however, the National Weather Service upgraded its rating to an EF-5, the highest category on the scale, with minimum wind speeds of at least 200 mph.
Tornadoes are rated by the type of damage they produce (their “strength”). Those rated in the EF-3 to EF-5 categories are considered to be the most “violent,” seemingly able to bend the laws of physics—pushing straws through thick tree trunks or scouring homes down to their foundations while leaving something as fragile as a small glass vase untouched in the same area. Fortunately, these types of monster storms are fairly rare.
According to NOAA’s National Climatic Data Center, an average of 1,253 tornadoes occur in the U.S. every year, with most of these tornadoes being categorized as “weak” (EF-0 to EF-1). “The remaining small percentage of tornadoes are categorized as violent (EF-3 and above). Of these violent twisters, only a few (0.1 percent of all tornadoes) achieve EF-5 status, with estimated winds over 200 mph and nearly complete destruction.” Given these statistics, about 20 tornadoes per year “can be expected to be violent and possibly one might be incredible (EF-5).”
Unfortunately for Moore, the “incredible” has now happened twice in 14 years, with the second EF-5 occurring Monday. Since the 1950s, there have been only 59 EF-5 tornadoes in the U.S. Moore now has the distinction of having been hit by two of those EF-5 tornadoes.
Many people in Moore who experienced the previous May 3, 1999, monster EF-5 tornado said that Monday’s tornado “appeared to be even worse.” The May 3, 1999, EF-5 tornado was also a mile wide, and produced an approximate recorded near-surface wind speed of 318 mph, the highest winds ever recorded. And like the May 3, 1999, monster EF-5, Monday’s tornado also tracked along a similar path.
So what is it about Moore that makes it so susceptible to such intense, violent storms? Could it all just be horrific coincidence or could it be its location?
Oklahoma leads the nation in the number of violent tornadoes per year, and Moore is situated within the crosshairs of Tornado Alley, which experiences more tornadoes than anywhere else in the world. During spring in this region, conditions are ideal for spawning tornadoes. Moist, warm air is drawn north from the Gulf of Mexico where it meets dry air coming down from the Rocky Mountains, which “lifts” it aloft. The clash of these different types of air masses creates atmospheric instability which can produce dangerous supercell thunderstorms. Supercells contain deep rotating updrafts called mesocyclones, which can and often do produce tornadoes. Considering all of these factors, it becomes easier to understand why this area is so susceptible to such violent storms.
Robert Henson, a science journalist and meteorologist working as an editor and writer at the National Center for Atmospheric Research in Boulder, Colorado, says that “It’s just the flat prairie of Oklahoma, with no particular features. Nobody’s established in science why one spot gets hit more than another. This is simply the terrible luck of the draw.” And for Moore, Oklahoma, that “terrible luck of the draw” played out on Monday.
Link to article in print: http://www.gcnlive.com/wp/2013/05/23/moore%e2%80%99s-eerie-history-of-tornadoes/
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