Two children are dead and one remains missing after a family’s vehicle got stuck crossing a swollen Arizona creek, authorities said Saturday as stormy weather hits holiday travelers around the country.

The Gila County Sheriff’s Office says it responded at about 4 p.m. Friday to Tonto Creek — about an hour and a half drive northeast from Phoenix — to find one adult on the shore and another stranded with four children on an island after escaping the “military-style” automobile. Volunteers and public safety officials scoured the area for the three missing children, surveying with helicopters, while crews with bulldozers worked to extract the half-submerged vehicle.

By midday Saturday, the bodies of a girl and boy, both age 5, were found three miles downstream, said Sheriff’s Lt. Virgil Dodd. But he said officials are hopeful they can rescue the last girl alive, as 30 people continue searching on foot.

The vehicle’s passengers, parents with their children and other young relatives, were in Tonto Basin to see family, according to Dodd. More details about the group’s reason for crossing were not immediately available, but local news outlets reported the family’s visit was part of a holiday gathering.

Intense winter weather is poised to snarl millions of U.S. travelers returning from Thanksgiving trips as what started as a West Coast storm expands east with snow, rain and strong winds. Earlier in the week, a record-breaking “bomb cyclone” hit the Pacific Northwest ahead of the holiday while snow and thunder rattled states to the center of the country and tornadoes arrived in the South.

The National Weather Service in Phoenix had warned Friday of flooding in Gila County, urging people to stay alert “even in locations not receiving rain.”

“Arroyos, streams, and rivers can become raging killer currents in a matter of minutes, even from distant rainfall,” the Weather Service said. It advised travelers to turn around if they hit swamped roads, saying most flood deaths happen in vehicles.

The flood warning remains in effect until 8:45 p.m. local time Saturday, and several Tonto Creek crossings have been closed, officials say.

Signs near where the family was rescued cautioned against entering the creek during flooding, Dodd said, adding that its waters will keep rising throughout Saturday. Barricades also discouraged attempts to drive through.

“There are people that do like to challenge Mother Nature when it comes to creeks and weather,” Dodd said. “We’d like to remind the public … when they see these signs, it’s very dangerous to attempt to cross.”

The sheriff’s office has not identified those involved.

Efforts to find the children have drawn on the resources of Tonto Rim Search + Rescue, a local volunteer group, as well as multiple sheriff’s offices and the Arizona Department of Public Safety.

Despite rushes and rocks, rough terrain and a swift current that complicate the work, authorities are “very optimistic” about the last child’s rescue, Dodd said.

Kim Bellware contributed to this report.