The National Weather Service has allowed tornado warnings issued earlier this evening to expire, but weather advisories remain in effect across the state.

The weather service has issued a tornado watch in 29 western Oklahoma counties effective until midnight.

The watch covers Alfalfa, Beaver, Beckham, Blaine, Caddo, Custer, Dewey, Ellis, Garfield, Grant, Greer, Harmon, Harper, Jackson, Kay, Kingfisher, Kiowa, Major, Noble, Nowata, Osage, Pawnee, Rogers, Roger Mills, Texas, Tulsa, Washington, Washita, Woods and Woodward counties.

The storms, which had been isolated and moving independently earlier in the evening, were beginning to merge and form a larger storm late tonight, according to the weather service. The storms were likely to move into central Oklahoma overnight, and it's possible the storms could be severe.

The chance for severe weather extends to Tuesday night statewide, according to the weather service.

No one has been reported hurt, but the storms caused light damage on Vance Air Force Base in Enid, according to the weather service. Two utility poles and some power lines were reported to be down there.

No injuries, damage from Blackwell tornado

At least one tornado has been reported so far on Memorial Day, according to the weather service.

About 6:45 p.m., storm spotters reported a tornado on the ground near Blackwell in Kay County moving northeast at about 25 mph, according to the weather service.

Dennis Bonewell, director of emergency management in Kay County, said he went to the area south of Blackwell where the tornado was reported, but he did not see any damage and no one had called in reports of damage elsewhere.

Power was out for 20 to 25 percent of Blackwell customers, Bonewell said.

Severe thunderstorm warnings in effect

- A severe thunderstorm warning is in effect in southern Osage County, eastern Pawnee County, northern Creek County and Tulsa County until 12:30 a.m. About 11:30 p.m., radar indicated a storm eight miles east of Mannford moving north at 22 mph, according to the weather service. Penny-sized hail and winds up to 60 mph are possible.

A severe thunderstorm warning is in effect in Payne County until 12:15 a.m. About 11:30 p.m., radar indicated a severe storm near Stillwater moving east at 30 mph. Half dollar-sized hail and winds up to 60 mph are likely.

A severe thunderstorm warning is in effect in northeastern Beckham County and southeastern Roger Mills County until 12:15 a.m. About 11:30 p.m., radar indicated a severe storm about 14 miles west of Elk City moving southeast at 21 mph, according to the weather service. Golf ball-sized hail and winds up to 60 mph are likely.

Flood danger in north, northeast Oklahoma

Because of heavy rain associated with the storms in Kay County, the weather service issued a flash flood warning there until 10 p.m. Storm spotters reported flash flooding was occurring near Braman and Blackwell, according to the weather service.

Additionally, the weather service issued a flash flood watch effective from 7 p.m. until Tuesday morning in 10 northeast Oklahoma counties because of heavy rain in Kansas and Arkansas, according to the weather service.

The watch covers Craig, Delaware, Mayes, Nowata, Osage, Ottawa, Pawnee, Rogers, Tulsa and Washington counties.

A flood warning is also in effect in Nowata County until Wednesday night, according to the weather service. The Verdigris River is expected to rise more than three feet above flood stage near Lenapah by Tuesday morning.

If the river rises by four feet or more, serious agricultural flooding between the Kansas state line and the headwaters of Lake Oologah will occur, according to the weather service.

Information from the Associated Press was used in this report.