Groups of large drones flying over eastern Colorado and western Nebraska have baffled law officers for more than a week, and reports continue to pour in.

About 30 drones have been flying over eastern Colorado each night, Lincoln County, Colo. Sheriff Michael Yowell said.

Yowell’s office is about 100 miles southeast of Denver in Hugo, Colo., but the drone sightings have not been confined to Colorado. There have been five reports of drones in Lincoln County, Neb. since Dec. 29, Sheriff Jerome Kramer said.

Lincoln County. Colo. received their first report on Dec. 26, but sightings really picked up Dec. 29 – just after a winter storm blew through — and have become a regular part of life since, Yowell said. Drones have been seen flying in pairs over several eastern Colorado counties. He said when you add it up, 4-6 drones per county; it totals 30 a night in eastern Colorado alone.

Phillips County Sheriff Thomas Elliot told the Denver Post that drones are flying in a grid pattern — flying one square and then another. Phillips County is east of Sterling.

Yowell said the flight paths are often random. He doesn’t know where they are coming from, but his office is investigating every possibility.

“No option is off the table,” he said. So far, investigators have reached out to state and federal law enforcement, the Department of Defense, as well as the private sector, with no success.

In an interview with the Bulletin, Yowell explained what they know about the drones. He said a sheriff’s sergeant saw one at a low altitude and estimated its wingspan was 54-60 inches (about five feet). He said the drones have been arriving around 7 p.m. and leaving around 10 p.m. each night. He said they leave towards the northwest, flying too quickly for anyone to follow. He said the drones are definitely unmanned, coordinated by electronics.

Yowell said two drone experts were consulted. Based on flight time and speed, they concluded the drones are a “hybrid style” of commercial and industrial quality. Their flight time is estimated at five hours. He said they might fly an hour to their destination, spend three hours “creeping around,” and another hour returning to home base. It was determined that type of drone costs $50,000. That would cover the cost of a basic model that can fly that long and at such high speeds.

He said there have been 24 confirmed sighting by law enforcement alone in his county — Lincoln County, Colo. — including the Limon Airport. No flight plans were filed for the mysterious machines.

The Federal Aviation Administration regulates drone flights, Yowell said, and sets a 400-foot ceiling. But on New Year’s Eve, he saw one well above that ceiling.

In the North Platte area, Lincoln County Sheriff Kramer said his office has processed five reports of drones in the last six days, including the most recent at 2:30 p.m. Thursday, Jan. 3 north of Sutherland, seen from the North River Road. That is the only daytime sighting that Kramer knows of.

“I haven’t had any UFO sightings in 30 years,” he said. “We are as eager as any one to have an answer. It leads to unrest, and that’s never good for our office.”

Kramer said drones have also been reported between Wellfleet and Dickens, from Sierra Drive north of Lake Maloney, near the North Platte Regional Airport, and south of Hershey near the intersection of the Hershey-Dickens Road and Walker Road. The latter sighting was around 8:30 p.m. on Jan. 2.

Numerous reports have come from Perkins County, Neb. One of those reports said wingspans are closer to six feet.

Federal agencies, police departments and sheriff’s offices are scheduled to meet on Monday, Jan. 6 in Brush, Colo. to confer and compare information, Kramer said.

“Something should surface soon,” he said.

Some counties have asked residents to stop reporting sightings unless they have a good picture, new details, or physical evidence.

Yowell said the news has spread far and wide. He’s been interviewed by the British Broadcasting Corporation as well as national news publications in the U.S.