CEMENT, Okla. (AP) The National Weather Service forecast a slight chance of tornadoes in parts of the Great Plains on Wednesday, and Oklahoma delivered.

A weak tornado touched down in southwestern Oklahoma after 3 p.m., according to weather services meteorologist Michael Scotten.

"We've had at least one confirmed tornado, for sure," he said, adding no one was hurt or injured. "It's mainly hit open areas out there."

The tornado touched down between Cement and Anadarko shortly after 3 p.m. Wednesday. The Chickasha school district, which was in the path of the tornado, kept its students after school as a precaution.

It's too early to tell how many storms could flare up or in which region, according to Richard Thompson at the Storm Prediction Center in Norman, Oklahoma, noting that the storms will likely be widely spaced apart.

"It's possible the hail at the very biggest could be tennis ball- or baseball-sized but that would be very isolated," Thompson said.

A swath of the Great Plains is under a tornado watch until 9 p.m. Wednesday, including parts of North Texas, Oklahoma, Kansas and Nebraska. Scotten also said the threat of weak tornadoes and hail was possible into Wednesday night.

"This is the first of potentially several days of a severe weather risk," Thompson said. "There could be some pretty heavy rain overnight and eventually flooding could be a concern."

Areas of central Oklahoma saw heavy rainfall and some flooding overnight and early Wednesday, National Weather Service meteorologist Jonathan Kurtz said. Nearly 4 inches of rain fell in Norman, where the Oklahoma Department of Transportation shut down several on-ramps to Interstate 35. The ramps re-opened early Wednesday afternoon.

"People just really need to stay weather aware, have a plan and understand that severe storms are possible across portions of the southern plains almost daily through Saturday," Kurtz said.