May 31 marks the anniversary of when the widest known tornado struck the El Reno, Oklahoma, area and claimed eight lives in 2013.
The El Reno tornado was on the ground for forty minutes during the evening of May 31, 2013, and traveled for 16.2 miles.
During that time, the tornado grew to become the widest known tornado on record with a maximum path width of 2.6 miles. The F4 Wilber-Hallam, Nebraska, tornado from May 22, 2004, originally held the record at 2.5 miles wide, according to AccuWeather.com Senior Meteorologist Alex Sosnowski.
Despite the width record, the [El Reno] tornado was not classified as an EF5 tornado (the highest ranking on the Enhanced Fujita Scale) by the National Weather Service (NWS).
"The tornado stayed mainly over farmland, thankfully, so there was a lack of damage found in the storm survey. Because of this, the tornado was rated an EF3, but wind speeds of EF5 or greater were measured," stated AccuWeather Meteorologist Becky Elliott.
"It had a peak forward speed of 55 mph, with wind speeds close to the surface of 295 mph measured by the Doppler on Wheels," added Elliott.
The storm had many smaller "sub-vortices" outside the main circulation and these were where the strongest wind speeds were recorded, Elliott said.
Elliott was among the many meteorologists who witnessed the volatile weather situation unfold across the southern Plains in advance of the El Reno tornado.
"I was working [at AccuWeather Enterprise Solutions] and as the day went on, all of us meteorologists were sitting there looking at the severe weather parameters and watching them going up," she said. "We all had that sick feeling in our stomachs because you knew it was going to be bad."
"I remember not chasing due to not wanting to chase in an urban area and feeling that [the metropolitan area of] Oklahoma City was the best target," Andrew Gagnon, AccuWeather Assistant Director of Storm Warnings.
Gagnon also remembers seeing the anvil or top of the supercell that produced the El Reno tornado from Wichita, Kansas, which is located about 150 miles to the north.
The tornado dissipated before reaching downtown Oklahoma City and spared El Reno and its airport from a direct hit. However, numerous homes and a few businesses were damaged.
Eight people were killed, all while in their vehicles. Among the dead was Storm Chaser and Engineer Tim Samaras.
"Finding out that Tim Samaras [had died] was very hard," continued Elliott. "That shocked the weather community since he was one of the safest chasers."
"It goes to show how erratic that tornado was. It wasn't anything that anyone could have predicted, how it expanded in size and then looped to the north. That is not something tornadoes typically do," she said.
The tornado was initially traveling to the southeast prior to abruptly turning northward.
The El Reno tornado formed in the warm and moist air mass that existed across central Oklahoma. Providing the trigger for the massive tornado was a stalled frontal boundary to the north and a push of dry air from the west.
There were more than 260 severe weather reports across the United States on May 31 with the most numerous from central Oklahoma to Indiana and Ohio.
The El Reno tornado not only impacted human lives, but researchers found that it stressed birds in the area to the point it became noticeable to biologists, AccuWeather Staff Writer Mark Leberfinger reported.