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.

Flood warnings were in effect Tuesday for 16 counties, including St. Louis County, where the Missouri and Mississippi rivers meet.

Officials said that the Mississippi River has topped a levee north of St. Louis and that the city of West Alton is in the final stage of an evacuation decree. The decree was issued Sunday, and while it remains voluntary, officials are saying the situation is urgent.

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

In central Missouri, the Lake of the Ozarks reached dangerously high levels, CNN affiliate KY3reported. That prompted officials to open the gates on the 148-foot Bagnell Dam to release 100,000 cubic feet of water per second.

Severe flooding can cause trouble for weeks to come, CNN meteorologist Pedram Javaheri said.

“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,” he said.

Over the weekend, eight people died in Missouri floods, including four 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.

Pulaski County Sheriff Ron Long said flash flooding can be particularly dangerous at night.

“Streams turn into rivers, and people sometimes don’t see the road has flooded over when they are driving at night,” he said.

 *Texas

Dallas-area residents trying to recover from a spate of deadly tornadoes will endure freezing temperatures Tuesday.

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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.”

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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.

Parts of northwest Massachusetts will probably get covered with a half-inch of ice Tuesday, the National Weather Service’s Boston office said.

“Sleet/freezing rain expected to be a greater concern than snow,” the office said.

But 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 12 inches of snow.

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The Southeast

After days of record warmth in the Southeast, temperatures will finally drop, CNN meteorologist Michael Guy said.

Parts of the South will get drenched with heavy rain and flooding, the National Weather Service said.

Georgia has already had at least one weather-related fatality. Authorities found a victim submerged in a vehicle in Gordon County, which has been hit hard by flooding.

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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.

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.

And the United States isn’t alone. The UK and South America are dealing with their own massive flooding.

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, like the major El Niño in 1997.

“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.”

CNN’s Brandon Miller, Nick Thompson, AnneClaire Stapleton, Alina Machado and Christine Sever contributed to this report.