A Record-Breaking Tornado
For the second time in two weeks, the state of Oklahoma has seen its second EF5 rated tornado.
Loop of storm-relative velocity imagery from the NWS-Norman Doppler radar from 6:00 to 6:19 p.m. CDT of the El Reno, Okla. tornado on May 31, 2013. Interstate 40 is depicted by the yellow line roughly west-to-east. (Images credit: Gibson Ridge)
After additional surveying and studying of weather data, including the use of information from mobile Doppler radar, the National Weather Service in Norman, Okla. has upgraded the May 31 tornado near El Reno, Okla. to an EF5. This is the highest possible rating a tornado can be given.
In addition, the width of the tornado has been given a "conservative" estimate of 2.6 miles. This is a new official record for the widest U.S. tornado, beating the previous record of 2.5 miles near Hallam, Neb. on May 22, 2004.
(However, research conducted by Joshua Wurman of the Center for Severe Weather Research suggests that similar radar-based measurement techniques would have justified a tornado width in excess of 4 miles for a tornado that struck Mulhall, Okla., on May 3, 1999. The official width of that tornado is listed as one mile, based on observed damage.)
This is the second EF5 rated tornado in Oklahoma in a matter of weeks. An EF5 tornado devastated nearby Moore, Okla. on May 20, 2013.
"This Was An Incredible Storm"
In a web conference held Tuesday, Rick Smith, warning coordination meteorologist at the National Weather Service in Norman, Okla., noted that this tornado was exceptional in many ways.
The massive tornado contained several powerful "subvortices," areas of extremely rapid rotation that swirled within the larger tornadic circulation. These subvortices contained the strongest wind speeds measured within the tornado, greater than 295 miles per hour in several different instances -- well above the 201-mph minimum requirement for a EF5 designation.
Not only did these subvortices contain almost unfathomable winds, but they were moving forward at incredible speeds, making them impossible to outrun.
"Think of the average size of an Oklahoma tornado you'd see on a typical afternoon - three or four of those things moving along the ground at a speed of 170 to 180 miles per hour, crossing each other with all kinds of violent motions going on," Smith remarked. "So this is going to be studied for a long time."
Smith later noted that a few of these vortices may have been moving along the ground at a jaw-dropping forward speed of 185 miles per hour, even as the parent tornado lumbered along at a forward speed of about 24 miles per hour.
"This was an incredible storm," Smith said. "The storm that produced this tornado was doing some phenomenal things."
"It Would Have Been Catastrophic"
Smith noted that the extreme winds associated with the subvortices affected a relatively small area compared to the tornado as a whole. None of the subvortices hit any structures, which is why mobile radar data from the University of Oklahoma were needed to assess the true strength of tornado; based on damage alone, survey crews could only find visual evidence of EF3 winds.
"They were relatively small -- some were very very small," Smith said of the intense subvortices. "It's quite possible that in a subdivision where you have big big lots that these could have passed between houses."
However, Smith noted that if any structures had been struck by this portion of the tornado, the result would have been "complete devastation."
Acknowledging the tragic toll on storm chasers and motorists caught in the erratic path of the tornado, Smith said, "The impacts were horrible ... but we were fortunate that this did not hit a densely populated area. I don't want to imagine ... but it would have been catastrophic."
Researchers Killed -- Stroke of Bad Luck?
The NWS report indicated that the two most intense subvortices with the highest wind speeds occurred "north and east of the intersection of 10th and Radio Road," approximately 3 miles south-southeast of downtown El Reno.
This location corresponds very closely to the last known location of Tim and Paul Samaras and Carl Young, the storm chasers and researchers who died while actively pursuing the tornado Friday evening.
Smith did not address questions about "storm chaser issues" in the conference, except to note that "a two-and-a-half-mile-wide tornado would not look like a tornado." As to whether any of the violent vortices within the tornado would have been visible, he added, "I could not begin to speculate."