Originally Published: 23 AUG 21 05:40 ET

Updated: 23 AUG 21 12:52 ET

By Ralph Ellis and Hollie Silverman, CNN

(CNN) -- Casey Hipshire knew flooding was possible, she said, but she thought the rainwater that filled the yard of her home in Middle Tennessee would recede. It didn't.

"All of a sudden it was like a tidal wave that just came over the road and into my yard," she told CNN.

Hipshire rushed to pack a bag and save herself, her 8-year-old son and her husband.

"Next thing I know the water is in my house, and it's up to my chest," she said.

"And my house fell off the foundation while we were still in it, so we had to break the window in the kitchen and crawl out of it and get up on the roof as fast as we could."

Hipshire's family survived the Saturday flash floods in Middle Tennessee that left at least 21 people dead and 40 people missing, authorities said Monday.

Twenty fatalities are from Waverly, a city of about 4,100 residents, and one was from Humphreys County, the Humphreys County Emergency Management Agency said.

Among those killed were 7-month-old twins, HCMA spokesperson Gray Collier told CNN on Monday. Details about the infants' deaths were not immediately available.

Rain inundated the region west of Nashville, sweeping away people, homes and vehicles as residents tried to escape. The flooding damaged infrastructure, schools, homes and other facilities in Waverly, Waverly Police and Fire Chief Grant Gillespie said during a Sunday afternoon news conference.

Some 2,000 homes in Humphreys County were without power around midday Monday, the emergency management agency said. About 10,000 customers in Middle Tennessee lost power in the weather event, CNN affiliate WSMV reported.

The number of people missing continues to fluctuate as names get added to the list while others are reported safe, Collier said, adding that the recent restoration of cell phone coverage led to an increase in reports of missing people. The agency reported 40 people missing on Monday morning, up from 25 missing late Sunday.

"We need patience and prayers," Humphreys County Sheriff Chris Davis said, adding people should stay out of the area as they continue their operations. Local officials are trying to craft a long-term plan, he said, but "we're getting overwhelmed."

The body of Davis' own best friend had been recovered, the sheriff revealed in a news conference.

"He drowned in this, and sitting here thinking about that, yeah, it's tough but we're going to move forward," Davis said.

Rescue and recovery efforts "will go on until we account for all missing Tennesseans," state emergency management agency Director Patrick Sheehan said.

"It's pretty devastating on the ground," Sheehan explained, adding, "We're going to see mostly recovery efforts at this point rather than rescue efforts."

Also among the dead is a foreman who worked on Loretta Lynn's ranch in Humphreys County, a Facebook statement from the country music legend said Sunday. Wayne Spears was the longtime foreman her property, the statement said.

"There are no words at the ranch today ... only tears. Our ranch family is our family," Lynn said in her Facebook post. "He took such good care of things here on the ranch for us. He's one of us and the whole Lynn family Is heartbroken. Please pray for his precious family and friends."

The Tennessee Health Department confirmed 16 deaths so far, Sheehan said, noting that the discrepancy with the toll reported by local authorities owes to the health department's strict process for validating deaths.

Rainfall may have set a Tennessee record

Saturday rainfall totals reached 17.26 inches north of Centerville, in Hickman County; 17.02 inches in McEwen, in Humphreys County; and 13.76 inches near Dickson, in Dickson County, the National Weather Service in Nashville said.

The rainfall total in McEwen may become a state record when it's made official, said Krissy Hurley, warning coordination meteorologist for Nashville weather service office. Centerville is not a verifiable weather station in terms of official records, the office told CNN.

"We were getting rainfall rates of 3 inches per hour for three hours straight," Hurley said. "It's an unheard-of, astronomical type of statistic to see after the fact."

The flooding on Saturday was caused by several storms training over the same area.

"We had a stationary boundary set up over western part of Middle Tennessee that provided the perfect set-up conditions, a constant training of (storms) over that one area for several hours right along that boundary," meteorologist Mark Rose from the Nashville weather service office told CNN.

"The rainfall forecast for this upcoming seven days shows almost nothing" for the area that flooded over the weekend, Rose said. "It's going to be a relatively dry week ahead."

Humprheys County schools close for the week

The flooding happened so quickly that the director of Humphreys County schools got trapped on the roof of Waverly Junior High, he said, WSVM reported.

"We had helicopters coming by, boats coming by, and we said y'all go to somebody else. We were fine. We were safe," Richard Rye said. "But to see some of the elderly and kids, like I said, I'm numb."

Rye canceled classes for the week, saying several buildings are in shambles and half the school buses are not operational. McEwen High School has become a reunification center for people displaced by the flood.

"Right now, I'm not worried about the schools," Rye told WSVM. "We'll rebuild, we'll clean them. We'll do what we've got to do to get our kids back to school, but right now we're worried about our kids."

Breaking through to the roof

Amanda Toungette Maples of Waverly described a harrowing escape from the floodwaters.

When the lowest room in her house began to fill with water, Maples headed to the garage to bring in her dog. The water rose so fast that, at some points, she had to swim back to the house with the dog in tow.

Going into survivor mode, she grabbed the most important electronics and got the animals into her home's highest room. The water just kept rising, so much so that the bed she was on began to float, she told CNN.

She called a police officer friend who urged her to get into the attic and break through to the roof, she said.

After busting through an air vent, Maples sat on the roof and watched water rise around her house -- and her mother's house across the road. She was terrified because her mother had no access to the attic after a home renovation had sealed it, Maples said.

Rescuers arrived on jet skis. Maples directed them first to save her mother, who -- Maples learned later -- had survived by standing on her kitchen island.

Governor mourns 'tremendous loss of life'

Tennessee Gov. Bill Lee surveyed the flood damage Sunday in Humphreys County and called it "a very tragic and difficult situation." He cited a different rainfall total.

The large amount of rain that fell -- a record 14 inches, according to the governor -- created "devastating flooding in the community" and a "tremendous loss of life," Lee said.

Lee spoke with survivors of the flooding and was shocked to hear how quickly their situation became dire, he said.

"They would see water in their yard and then within minutes it was coming into their home," Lee said, adding residents went from "seeing floodwaters rise to not being able to escape their homes."

Lee described the aftermath as tragic: "Homes washed off their foundations, cars strewn about the community. It is a devastating picture of loss and heartache," he said.

First responders, including the National Guard, will remain on the scene as search and rescue operations continue, the governor said.

"What we do know is that it's incredibly difficult, and our hearts and our prayers need to be for these communities, for those folks in that community, many of them who have suffered not only the loss of their homes and their property but the loss of family members and friends," Lee said.

Sheriff describes pain of being unable to help everyone

As emergency responders tried Saturday night to get into the flood zone, their effort was complicated by downed phone lines and washed-out roads, said Davis, the Humphreys County sheriff.

He likened it to the feeling of a mother not being able to reach her child.

"Knowing that you have people that stayed that can't get help ... I have people floating down the creek that nobody can get to, and nobody can help. It hurts. It hurts," he said, holding back tears.

Waverly Mayor Buddy Frazier said the loss of life is unlike anything the town has ever experienced.

"I've been around a long time, and I've been through a lot of events here and this one really took me back," Frazier said. "This is bad, this is bad: the number of people it affected the number of lives lost."