As Wednesday began, 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 supercell storms to form.“The conditions grew more favorable,” National Weather Service meteorologist Dan Shoemaker said.From that seemingly slight chance of twisters came the deadliest tornado to strike the Dallas-Fort Worth area 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 in the area since 10 people were killed in Dallas on April 2, 1957. The deadliest tornadoes in Texas history happened May 11, 1953, when an EF5 twister killed 114 and injured 597 in Waco and in Goliad on May 18, 1902, which killed the same number of people and injured 250.The Granbury twister was also North Texas’ first EF4 tornado, capable of producing winds of 166 to 200 mph, since the tornado that struck Lancaster in southern Dallas County on April 25, 1994. It killed three people and destroyed more than 200 houses.After the Granbury tornado fell apart, the same storm produced an EF3 tornado that hit the Cleburne area, causing 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 was keyWednesday’s storms produced at least 16 tornadoes, stretching from Montague County, near the Red River, to Hamilton and Coryell counties in Central Texas.A variety of factors apart from intensity contributed to how deadly the storm was.“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. “Anytime tornadoes occur at night or close to nightfall, the risk factors go up significantly.”Weiss pointed to an EF5 tornado in Greensburg, Kan., on May 4, 2007, as an example of a killer storm that struck at night. Eleven people were killed as the tornado leveled most of the small town.The path of Wednesday’s storm also played a role as it traveled over populated areas in Hood and Johnson counties. They’re not as densely populated as Tarrant and Dallas counties, but the areas have far more people than other nearby places where the storm could have 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 in 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 Huckaby. 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 were 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 officials had some warning and were able to alert residents.The advance warning system included the Code Red phone notification system, which made about 18,000 calls Wednesday night. That was in addition to sirens and the reports on TV, radio and social media.Deeds said the warning system was activated 10 to 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.She was standing outside with her neighbor when it started hailing and she went inside her neighbor’s home.“We saw the hailstorm 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.” Staff writers Terry Evans and Patrick M. Walker contributed to this report.
ENHANCED FUJITA SCALEThe rating system used for tornadoes• EF5: Winds over 200 mph• EF4: 166-200 mph• EF3: 136-165 mph• EF2: 110-135 mph• EF1: 86-109 mph• EF0: 65-85 mphSource: National Weather Service
Bill Hanna, 817-390-7698 Twitter: @fwhanna