The tornado's unusual behavior consisted of these simultaneous occurrences: abrupt changes in direction, rapid enlargement to a width of 2.6 mi (4.2 km) in diameter in about 30 seconds, swift increase in forward motion from about 20 to 55 mph (32 to 89 km/h) within a few minutes, multiple vortices within and around, and an expansive translucent outer circulation without a full condensation funnel while being surrounded and obscured by precipitation made it a worst-case scenario for storm chasers.
Several professional and amateur chasers were caught off guard and impacted by the tornado.
Many were located in a region northeast of the tornado, known as the "bear's cage".
Chasers can generally get a clear view of the tornado from that area; however, it places them at great risk and with little time to react should the storm take a left turn.

In the case of El Reno, the wrapping rain bands did not lead to a narrow corridor of clear air close to the tornado.
Rather, these rotating curtains of rain were the outer circulation of the tornado itself.
Former Discovery Channel storm chaser Tim Samaras (an engineer), his son Paul Samaras (a photographer), and Tim's longtime chase partner Carl Young (a meteorologist), all professional storm chasers with the TWISTEX project, were caught directly by the tornado; all three died in their vehicle, two of them were ejected.
Normally, Tim drove a reinforced three-quarter ton truck optimized for hail protection and stability in high winds; however, on May 31, Carl was driving an unmodified Chevrolet Cobalt, a subcompact vehicle with three 45-lb barometric probes in the trunk likened by one TWISTEX chaser to a "pizza delivery car", making it much less suited to high winds and rain-slicked backcountry dirt roads.
It was also underpowered, which hampered their escape in the strong inflow winds.
Tim's body was found still buckled in the passenger's seat.
They were the first known tornado-related deaths of either recreational storm chasers or scientific researchers.

Mike Bettes, a meteorologist for The Weather Channel, was also caught in the storm.
His sport utility vehicle was severely damaged, having been thrown about 200 yards (180 m); the driver was left with a broken neck, fractured vertebrae, and several broken ribs while Bettes and the other passenger sustained minor injuries.
Meteorologist Emily Sutton and storm chaser Kevin Josefy of Oklahoma City NBC affiliate KFOR-TV (channel 4) were also caught in the path of the storm; their vehicle was damaged by debris hurled by the tornado.
University of Oklahoma student Billy Prater, along with his father and a friend, sought refuge under an overpass (an action strongly discouraged in these situations) when the tornado changed direction.
Near Union City, debris from a barn destroyed by the tornado struck the vehicle of Brandon Sullivan and Brett Wright, breaking their windshield; they escaped without injury.
The hood of Reed Timmer's Dominator 2, a vehicle designed for intercepting tornadoes, was torn off.
Storm chaser Dan Robinson received injuries after being enveloped within the outskirts of the tornadic circulation.
He escaped a few hundred meters ahead of the TWISTEX crew and is believed to be the last person to see Samaras, his son Paul and Young.

A Doppler on Wheels-based analysis of how the tornado impacted these teams revealed that they were hit by an intense internal sub-vortex.
This analysis showed that both the Weather Channel and TWISTEX vehicles entered the tornado through the less intense north/northwestern side, then were impacted by the internal sub-vortex, which contained radar-indicated winds approaching 200 miles per hour (320 km/h) and was moving in a complex quasi-trochoidal pattern, sometimes nearly stationary, sometimes with forward speeds over 100 miles per hour (160 km/h).
Entering the larger tornadic circulation without the ability to maintain situational awareness of the internal sub-vortex was likely a key contributing factor to the deaths and injuries.
The tornado's unusual behavior consisted of these simultaneous occurrences: abrupt changes in direction, rapid enlargement to a width of 2.6 mi (4.2 km) in diameter in about 30 seconds, swift increase in forward motion from about 20 to 55 mph (32 to 89 km/h) within a few minutes, multiple vortices within and around, and an expansive translucent outer circulation without a full condensation funnel while being surrounded and obscured by precipitation made it a worst-case scenario for storm chasers. Several professional and amateur chasers were caught off guard and impacted by the tornado. Many were located in a region northeast of the tornado, known as the "bear's cage". Chasers can generally get a clear view of the tornado from that area; however, it places them at great risk and with little time to react should the storm take a left turn.
In the case of El Reno, the wrapping rain bands did not lead to a narrow corridor of clear air close to the tornado. Rather, these rotating curtains of rain were the outer circulation of the tornado itself. Former Discovery Channel storm chaser Tim Samaras (an engineer), his son Paul Samaras (a photographer), and Tim's longtime chase partner Carl Young (a meteorologist), all professional storm chasers with the TWISTEX project, were caught directly by the tornado; all three died in their vehicle, two of them were ejected. Normally, Tim drove a reinforced three-quarter ton truck optimized for hail protection and stability in high winds; however, on May 31, Carl was driving an unmodified Chevrolet Cobalt, a subcompact vehicle with three 45-lb barometric probes in the trunk likened by one TWISTEX chaser to a "pizza delivery car", making it much less suited to high winds and rain-slicked backcountry dirt roads. It was also underpowered, which hampered their escape in the strong inflow winds. Tim's body was found still buckled in the passenger's seat. They were the first known tornado-related deaths of either recreational storm chasers or scientific researchers.
Mike Bettes, a meteorologist for The Weather Channel, was also caught in the storm. His sport utility vehicle was severely damaged, having been thrown about 200 yards (180 m); the driver was left with a broken neck, fractured vertebrae, and several broken ribs while Bettes and the other passenger sustained minor injuries. Meteorologist Emily Sutton and storm chaser Kevin Josefy of Oklahoma City NBC affiliate KFOR-TV (channel 4) were also caught in the path of the storm; their vehicle was damaged by debris hurled by the tornado. University of Oklahoma student Billy Prater, along with his father and a friend, sought refuge under an overpass (an action strongly discouraged in these situations) when the tornado changed direction. Near Union City, debris from a barn destroyed by the tornado struck the vehicle of Brandon Sullivan and Brett Wright, breaking their windshield; they escaped without injury. The hood of Reed Timmer's Dominator 2, a vehicle designed for intercepting tornadoes, was torn off. Storm chaser Dan Robinson received injuries after being enveloped within the outskirts of the tornadic circulation. He escaped a few hundred meters ahead of the TWISTEX crew and is believed to be the last person to see Samaras, his son Paul and Young.
A Doppler on Wheels-based analysis of how the tornado impacted these teams revealed that they were hit by an intense internal sub-vortex. This analysis showed that both the Weather Channel and TWISTEX vehicles entered the tornado through the less intense north/northwestern side, then were impacted by the internal sub-vortex, which contained radar-indicated winds approaching 200 miles per hour (320 km/h) and was moving in a complex quasi-trochoidal pattern, sometimes nearly stationary, sometimes with forward speeds over 100 miles per hour (160 km/h). Entering the larger tornadic circulation without the ability to maintain situational awareness of the internal sub-vortex was likely a key contributing factor to the deaths and injuries.
2013 El Reno tornado