(UPPER MAKEFIELD, Pa.) — A search for a 2-year-old girl and her 9-month-old brother who were washed away with their mother in a flash flood in Bucks County, Pennsylvania, is expected to be scaled back on Wednesday after officials said rescue crews combed the entire flood zone more than a dozen times.

Severe weather Wednesday morning in the search area was delaying rescue crews from resuming the search for 2-year-old Matilda “Mattie” Sheils and her 9-month-old Conrad Sheils, according to the Upper Makefield, Pennsylvania, Police Department.

“The area and conditions will be continuously monitored throughout the day and if we are able to deploy our assets, we will do so. This setback has us all frustrated as we are desperate to bring Mattie and Conrad home,” police officials said in a statement.

The children have been missing since Saturday afternoon when they and their family were caught in the deluge while driving on Route 532 to a barbecue, authorities said.

The children’s mother, 32-year-old Katie Seley, died after she grabbed Mattie and Conrad and tried to escape their vehicle but ended up being swept away in the violent weather event near Upper Makefield Township, officials said.

Seley was among five people killed in the storm. Her body was recovered on Sunday.

Rescue crews are expected to scale back the search on Wednesday after more than 100 emergency personnel spent the past four days scouring the flooded area along Hough’s Creek, Chief Tim Brewer of the Upper Makefield Fire Company said. He said crews have used cadaver dogs in ground searches of the creek’s banks and have deployed sonar equipment and drones to search the creek, a tributary that leads to the Delaware River.

“We have searched the entire flood zone more than a dozen times,” Brewer said at a news conference Tuesday afternoon, adding that the search covered roughly 117 acres.

Brewer said the focus of the search will switch on Wednesday to a “dive rescue operation.”

“That will mean underwater assets mainly in the creek and we will work out from there. We still have K-9 assets in place, but we are going to begin to scale down,” said Brewer, adding that crews have searched and re-searched the area.

“Tracking logs are over 160 miles, meaning we have backtracked several times,” Brewer said.

The tragedy unfolded around 5:30 p.m. Saturday when more than 7 inches of rain fell within 45 minutes, causing Hough’s Creek to spill its banks and generating a “wall of water” that took drivers on Route 532, also known as Washington Crossing Road, by surprise, Brewer said. He said 11 cars were washed away in the flash flood and at least one was found 1.5 miles from where it was swept into the creek.

The missing children and their family are from South Carolina and were in Pennsylvania visiting friends and relatives when disaster struck.

Mattie and Conrad’s father, Jim Sheils, and their grandmother grabbed ahold of the missing siblings’ 4-year-old brother and escaped their car as it and other vehicles were being washed away, according to officials. The father, grandmother and 4-year-old were found alive, officials said.

“They were caught in a flash flood,” Brewer said. “The wall of water came to them, not the other way around.”

Besides Katie Seley, four other people were confirmed dead in the Bucks County flooding. They were identified by the Bucks County Coroner’s Office as Enzo Depiero, 78, and Linda Depiero, 74, both of Newtown Township, Pennsylvania; Susan Barnhardt, 53, of Titusville, New Jersey; and Yuko Love, 64, of Newtown Township.

The coroner’s office said all of the victims died from drowning.

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