Torrential storms flooded parts of central Texas early Wednesday, stranding people on roofs, in trees and in vehicles, and the weather was so treacherous that some helicopter rescue attempts had to be abandoned.

The worst flooding was in Williamson, Lampasas and Burnet counties in the Texas Hill Country northwest of Austin.

"We got hard facts of 18-plus inches of rain in a couple of those places since midnight," Austin-Travis County emergency medical services spokesman Warren Hassinger said just after 7 a.m. More rain was expected throughout the day, the National Weather Service said.

Parts of Oklahoma also were soaked Wednesday, with rain falling on Oklahoma City for the 15th consecutive day, breaking a 70-year-old record.

Hassinger's agency had reports early Wednesday of at least 20 trapped atop vehicles, on roofs or clinging to trees surrounded by fast-moving water.

However, the weather was so stormy that helicopter crews had to abandon several rescue attempts, Hassinger said. He said four rescue attempts were halted before dawn and he didn't know what happened to the people needing help.

One aborted rescue mission had attempted to get four people from the roof of a house in Granite Shoals, where water was about 4 feet from the top of the building. They had pulled a possible drowning victim from the water, Hassinger said.

One successful helicopter-assisted rescue plucked a Williamson County sheriff's deputy and another person from atop the lawman's car along the San Gabriel River near Georgetown, Hassinger said.

Ray Thomas and his wife fled their house on a peninsula between the North and South San Gabriel rivers at about 4:45 a.m., after hearing an emergency weather radio bulletin.

"We're lucky we got out," he said. "In September we were praying for rain. What worries me now is the rain that's still to come."

Texas and Oklahoma also were hit by heavy rain Tuesday.

Residents of at least 50 homes had to be evacuated from a flooded subdivision near Lake Granbury, about 60 miles southwest of Dallas. Rescuers used boats and jet skis to remove those residents late Tuesday as Robinson Creek rose out of its banks.

About 30 evacuees spent Wednesday morning at the First United Methodist Church in Granbury, the Rev. Neil Norman said.

"There's some shock because the water must have come up extremely quickly," Norman said. "This is all pretty much hard to believe."

In Oklahoma, about 20 firefighters had to use a raft to rescue 16- year-old twin sisters from their car, stalled in rushing bumper-deep water Tuesday.

The Oklahoma City area received about an inch of rain in 24 hours, bringing the city's annual total to 28.03 inches - about 10 inches above normal. Flooding closed some roads Wednesday in central and northeastern Oklahoma.

"Anytime it rains there's going to be the threat of heavy downpours, it's not out of the question for any one area to get three inches," weather service meteorologist Ty Judd said Wednesday in Norman, Okla.

A 13-year-old boy died in the Dallas suburb of Garland Tuesday night after being washed down a flooded creek, police spokesman Joe Harn said. The boy was swept away when firefighters using ropes tried to pull him ashore from a bridge pillar where he was stranded. He was found a mile downstream about two hours later, Harn said.

A number of flood warnings were posted throughout Texas. North Bosque River near Clifton was expected to crest at almost 29 feet early Wednesday, which is about 6 feet above normal and the highest since a crest of 28.9 feet in 1977.

Elsewhere, several Chicago streets and basements were flooded as parts of the city received 3 to 4 inches of rain in about 45 minutes, just before Tuesday's evening rush hour, according to the National Weather Service.

The water department received more than 700 reports of flooded basements, officials said.