Weather Channel meteorologist Dr. Greg Forbes examines the dangerous tornado outbreak that may lead to a violent Saturday.
Updated at 11:55 p.m. ET: Forecasters are warning of a major tornado outbreak in Kansas and Oklahoma this weekend, with Oklahoma getting a first taste of it on Friday with a tornado touching down near the National Weather Service office in Norman.
A tornado touched down near the University of Oklahoma campus in Norman just after 4 p.m. local time - the same town that holds the National Storm Prediction Center, the National Weather Service confirmed.
An operator at the University of Oklahoma said people had been warned to get to a basement or low floor.
"I was watching this tornado on TV, which was neat until I realized it was right here in Norman," said the operator, who did not give a name.
Video from television helicopters showed the tornado ripped roofs from buildings, downed power lines and uprooted trees in the city of about 100,000 about 20 miles south of Oklahoma City, but Oklahoma Department of Emergency Management spokeswoman Keli Cain said there were no reports of serious injuries.
"This is just a fraction of what's to come tomorrow," Chris Vaccaro, a spokesman for the National Weather Service, warned.
Noaa / AP
This graphic, provided Friday by NOAA's Storm Prediction Center, shows areas at risk of severe weather in Kansas and Oklahoma on Saturday.
Norman Regional Hospital and an affiliate treated 19 people for mainly "bumps and bruises," and one patient remained hospitalized in fair condition late Friday, hospital spokeswoman Kelly Wells said.
Atmospheric conditions for the weekend will be similar to those that caused severe storms in parts of the Midwest and Southeast in early March that killed more than 50 people, said Steve Weiss, science support branch chief for the National Storm Prediction Center.
"We see potentially some ... very damaging tornadoes," Weiss said.
Oklahoma was already having severe weather Friday -- but the biggest storms are expected Saturday, said Weiss, who was watching heavy rain out of his office window in Norman on Friday afternoon. "It's not unusual to have successive days," he said.
Conditions favor strong thunderstorms in Kansas and Oklahoma on Saturday, with a few "supercell" storms with rotating updrafts, Weiss said.
"The potential is that some of the supercells could be long-lived, so if they produce tornadoes they could be on the ground for a while," he said.
Forecasters said the storms could start Saturday afternoon into the early evening and continue after dark.
"The really dangerous part is that it looks like it's going to be overnight," said Kurt Van Speybroeck, emergency response meteorologist for the National Weather Service. "It's a really bad combination to get tornadoes at night because they're harder to see. It could be a really bad evening."
Storms could strike heavily populated areas such as Oklahoma City, and Wichita and Topeka, Kansas, Weiss said.
The high-risk area is from about the I-40 highway in Oklahoma City going north along I-35 to I-70 in central Kansas, said Van Speybroeck.
Northwest Texas into Nebraska and parts of Iowa and Missouri are also at risk for thunderstorms and tornadoes this weekend.
Reuters and The Associated Press contributed to this story.
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