(CNN) The storm is over but the flooding is nowhere near ready to subside.

Many people in the central and Southern United States are looking out their windows and wondering whether the water will take their homes.

For some, it is beyond that time.

More than 18 million Americans live in areas under flood warnings, the National Oceanic and Atmospheric Administration said Tuesday. Thirteen states are affected, NOAA said.

One of the states most affected is Missouri, which is grappling with deadly flooding that will threaten cities and towns along rivers for days even through the most of the rain has stopped.

Levees have been overtopped in West Alton, just north of St. Louis. And late Tuesday, St. Charles County emergency officials ordered all people to evacuate the mostly rural area, which lies on the Mississippi River.

On the other side of the river, downstream, in Illinois, a prison has partially evacuated. Menard Correctional Center lies on the banks of the Mississippi, and staff anticipates minor flooding in some of its cells, when the river crests.

There have been an estimated 49 weather-related deaths in the past week across the country, with the current severe storm system blamed for 35 deaths: 13 in Missouri, 11 in the Dallas area, five in southern Illinois, five in Oklahoma and at least one in Georgia. Many died after their cars were swept away by floodwater.

Here's what to expect across the country:

Missouri

The rain has ended, but Missouri will still have "major to historic river flooding through early next week," the National Weather Service's St. Louis office said.

Lauren Mueller, a resident of one of the areas affected by floods, said that a park in St. Charles County was underwater. "Ducks are swimming where my feet were two weeks ago," she said.

Much of Union is in imminent danger of being flooded. Russell Rost, an emergency management official, said that the town has been cut in half by floodwater.

Mayor Mike Livengood said 25 homes in the town were affected after the Bourbeuse River reached record height.

Major and historic flooding is expected along area rivers. Never drive into flood waters! #stlwx #mowx #ilwx pic.twitter.com/riifGfQOYs — NWS St. Louis (@NWSStLouis) December 29, 2015

Gov. Jay Nixon activated the National Guard to aid first responders and provide security in evacuated areas. The governor said that when the Mississippi River crests Wednesday night or Thursday morning, it will be at its highest level ever, beating the record flooding of 1993.

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"We know just by nature of how volumes of water move downstream ... it'll take weeks for the water to work its way downstream and really inundate communities," said CNN meteorologist Pedram Javaheri.

Of the at least 13 people who have died in Missouri floods, five were international soldiers temporarily stationed at Fort Leonard Wood for training.

A witness reported the soldiers' car driving onto a flooded road and immediately getting swept downstream, the Pulaski County Sheriff's Office said. The names and nationalities of the four soldiers have not been released.

Texas

Dallas-area residents trying to recover from a spate of deadly tornadoes endured cold temperatures Tuesday. The low was expected to be 36 degrees Wednesday morning.

Photos: Dallas-area tornadoes Photos: Dallas-area tornadoes Josh White gets emotional as he recounts how he lived through the tornado that hit Garland, Texas, on Saturday, December 28. The National Weather Service confirmed that three tornadoes were part of storms that ripped through the Dallas area, killing 11 people and damaging hundreds of buildings. Hide Caption 1 of 12 Photos: Dallas-area tornadoes An emergency vehicle drives through a neighborhood in Rowlett, Texas, on Sunday, December 27. Crews were scouring debris for victims and assessing damage. Hide Caption 2 of 12 Photos: Dallas-area tornadoes Bob Moore walks through his home in Rowlett the morning after it was hit by a tornado. Hide Caption 3 of 12 Photos: Dallas-area tornadoes A Christmas tree lies in the wreckage of a family's home in Rowlett on December 27. Hide Caption 4 of 12 Photos: Dallas-area tornadoes A bus is overturned in Garland on December 27. Hide Caption 5 of 12 Photos: Dallas-area tornadoes Debris is scattered around a driveway in Rowlett on December 27. Hide Caption 6 of 12 Photos: Dallas-area tornadoes Tornado damage is seen in a neighborhood in Garland on December 27. Hide Caption 7 of 12 Photos: Dallas-area tornadoes A Rowlett home is heavily damaged. Hide Caption 8 of 12 Photos: Dallas-area tornadoes This apartment building in Garland was damaged as well. Hide Caption 9 of 12 Photos: Dallas-area tornadoes Michael Downard stands outside his house in Rowlett the morning after it was struck by a tornado. Hide Caption 10 of 12 Photos: Dallas-area tornadoes Damage is seen in a Garland neighborhood on December 27. Hide Caption 11 of 12 Photos: Dallas-area tornadoes A flipped vehicle is seen in Rowlett. Hide Caption 12 of 12

But a lot of people are more concerned with where they are going to live for now. Many have been displaced from their homes after several tornadoes, including one in Garland that killed eight people.

"I feel so bad for my kids because everything they were so excited for (at Christmas) is gone now," Garland resident Terri Sykora said.

David Ruiz survived the tornado in Garland, but his house did not. Amid all the rubble, his family's two cats are still missing.

"You don't know how to recover yet," he said. "Thankfully, a lot of family has sent a lot of money so that we can recover. And we're able to eat and stay somewhere warm with a friend."

The Upper Midwest and Northeast

The storm will continue dumping heavy snow and ice across the Northern and Central Plains, Great Lakes and the Northeast, the National Weather Service said.

A freezing rain advisory was issued for parts of northwest Massachusetts, the agency said, but it was canceled Tuesday night.

"But cold air/wet surfaces still mean icy spots on roads & walkways. Be cautious overnight and Wednesday," the Boston office of the NWS tweeted.

Freezing Rain Advisory cancelled. But cold air/wet surfaces still mean icy spots on roads & walkways. Be cautious overnight and Wednesday. — NWS Boston (@NWSBoston) December 30, 2015

North of Massachusetts, it's a different story.

Much of Vermont and New Hampshire will see 4 to 6 inches of snow, and much of Maine could get pummeled with 8 to 14 inches of snow, forecasters predict.

Blame it on El Niño

At least 69 tornadoes have touched down in the United States in just the past week, Javaheri said.

"Typically, you see about 24 for the entire month of December," he said.

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But flooding causes many more deaths in the country than tornadoes do. And there have already been about 400 reports of rivers flooding in the country.

In some places, the rainfall hasn't stopped for weeks. Portland and Seattle have been drenched with rain every day in December, Javaheri said.

Blame it on El Niño , a warming of the eastern Pacific Ocean, mainly along the equator.

El Niños occur every two to seven years in varying intensity, and the waters of the eastern Pacific can be up to 4 degrees Celsius (7 degrees Fahrenheit) warmer than usual.

El Niños can cause more frequent and intense storms, as well as massive economic damage, as the major El Niño in 1997 did.

"Globally speaking," Javaheri said, "this is something that typically has somewhere around $30-$45 billion of damage that at least occurred the last go-around in 1997 into 1998."