By The Fort Worth Star-Telegram
May 17, 2013

At the beginning of the day Wednesday, the possibility of deadly tornadoes didn`t appear likely across North Texas.

But as the day progressed, the ingredients quickly fell into place. There was enough wind shear. West of Fort Worth, the skies were clear, which produced enough heating for the super cell storms to form.

"The conditions grew more favorable," said National Weather Service meteorologist Dan Shoemaker.

From that seemingly slight chance of twisters came the deadliest tornado to strike North Texas in more than 50 years.

At least six people died Wednesday night when a tornado tore through the Rancho Brazos neighborhood near Granbury, the most since 10 people were killed in Dallas on April 2, 1957. The deadliest tornado in Texas history came May 11, 1953, when an EF-5 twister killed 114 and injured 597 in Waco.

The Granbury twister was also North Texas` first EF-4 tornado, capable of producing winds of 166-200 mph, since the April 25, 1994, tornado that struck Lancaster in southern Dallas County, which destroyed more than 200 houses and killed three people.

After the Granbury tornado fell apart, the same storm produced an EF-3 tornado that hit the Cleburne area, with the most significant damage just east of Lake Pat Cleburne.

"It looks like it dissipated and then re-formed," Shoemaker said. "It may have re-formed a couple of times."

Time of day a key factor

Wednesday`s storms produced at least 10 tornadoes that stretched from Montague County, near the Red River, to Hamilton and Coryell counties in Central Texas.

Why the tornado was so deadly was likely due to a variety of factors.

The intensity of the Granbury tornado certainly played a role but there were other factors that came into play.

"I think clearly one of the major factors was the time of day," said Christopher Weiss, associate professor of atmospheric science at Texas Tech University. "Any time tornadoes occur at night or close to nightfall, the risk factors go up significantly."

Weiss pointed to the May 4, 2007, EF-5 tornado that struck Greensburg, Kan., as an example of a killer storm that struck at night. In that one, 11 people were killed as the tornado leveled most of the small Kansas town.

The path of the storm also played a role as it traveled over populated areas in Hood and Johnson counties. Though it isn`t as densely populated as Tarrant and Dallas counties, it has far more people than other nearby rural areas where it could touched down.

"I can`t think of a worse path through Granbury and Cleburne," Weiss said. "It traveled through some fairly populated areas, which always plays a significant factor."

The storms started forming west and northwest of Fort Worth late Wednesday afternoon.

Miguel Chavarria, a member of the Quad County Storm Chasers out of North Texas, followed the Granbury storm as it moved in from the west.

He and other storm chasers followed a "constantly turning wall cloud," arriving just before the tornado struck the Rancho Brazos subdivision.

"We chased it down here from Lipan," he said. "It formed between Stephenville and Lingleville and followed Farm Road 219 to Huckabee. Then it turned toward Lipan and when it got to Highway 4 it literally made a U turn and came back to Granbury."

Sirens were wailing as the storm chasers pulled into Granbury, Chavarria said. The tornado hit about 10 or 15 minutes later.

`Maybe this is serious`

Weiss, the Texas Tech associate professor, said the Storm Prediction Center and the National Weather Service`s Fort Worth office responded quickly as conditions changed with the storm.

"What happened was there stronger winds aloft than initially forecast," Weiss said. "There was enough increase in that intensity that it alerted forecasters that supercell systems could form. I think they did a good job of reacting and if you look at the advisories that went out, they certainly upped the risk for tornadoes forming and got the word out."

Hood County Sheriff Roger Deeds said they had advance warning of the storms approach and were able to alert residents.

The advance warning system included the Code Red phone notification system, which sent out about 18,000 calls Wednesday night. That was in addition to warning sirens and the reports on TV, radio and social media platforms.

Deeds said the warning system was activated 10-15 minutes before the twister struck.

Asked whether the warnings made a difference, he said, "I believe it did."

But some, such as Rancho Brazos resident Arlena Sherman, said she had no idea what was coming as the storm approached.

She was standing outside with her neighbor when it started hailing and then went inside her neighbor`s home.

"We saw the hail storm come in and then the power went out," Sherman said. "When the trees blew flat, we went inside. We heard the sirens and were like `maybe this is serious.` But it only lasted about two minutes, then it was over. It was just horrific when we outside. It was unimaginable all of the devastation around us. Homes were flattened. People were screaming, pinned or trapped in their homes. It was just terrible."

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(c)2013 The Fort Worth Star-Telegram

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Story image: A toppled car lies next to crushed trees in the Rancho Brazos neighborhood of Granbury, Texas on Thursday, May 16, 2013. AP Photo/The Fort Worth Star-Telegram, Paul Moseley

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