BILLINGS, Mont. - Flooding disrupted emergency phone service across a broad swath of eastern Montana on Monday as areas of the state remained inundated and downstream communities prepared for the worst.

In southeast South Dakota, residents of the small town of Dakota Dunes were told to be ready to leave their homes by Thursday - and prepare to be gone awhile - as the Missouri River continued to rise.

"Residents should plan to be away from their homes for as long as two months," said Eric Stasch, operations manager at Oahe Dam upstream in north-central South Dakota.

Gov. Dennis Daugaard stressed that the town's 2,500 residents were only advised to be ready and had not been ordered to evacuate.

Meanwhile, heavy showers again pounded parts of Montana after more than a week of record-breaking rain. That added more water to flooded rivers and streams that had started to recede over the weekend.

Snow was falling in the mountains and warm weather forecast for later in the week was expected to trigger a new round of flooding as the spring melt begins.

Authorities said northwestern Montana and downstream states including the Dakotas were next in line for high water problems.

"This could be a pretty significant week for flooding, and it might expand," said Monique Lay, spokeswoman for the Montana Emergency Coordination Center.

In Dakota Dunes, S.D., moving trucks became a common site over the weekend.

"We already got everything out of our basement," Jefferson Galvin told KMEG-TV on Sunday. "My dad and my uncle are ripping up the carpet right now."

Stasch said many levees being built in the Pierre-Fort Pierre area to protect public infrastructure also will shield private property. But he said residents in flood-threatened areas should not assume the levees will be done in time or hold against the record dam releases.

Another 200 South Dakota National Guard soldiers were called to help battle flooding along the Missouri River, bringing the total to more than 600 by Tuesday.

Soldiers also have been called out in parts of Montana and Wyoming.

In North Dakota, officials voted to build a temporary levee at one Bismarck neighborhood, while police officers went door-to-door in another, telling residents to be prepared to leave. No evacuation was ordered, and city spokeswoman Gloria David said there was no timeline for a decision.

Residents also prepared for flooding along the river in Nebraska and Iowa, where water has already spilled over the banks in several low-lying areas.

A riverside subdivision near the northwest Iowa city of Sloan called for help filling sandbags, while residents of the northeast Nebraska cabin community of Lazy River Acres left their homes Sunday before floodwater could block their escape.

Knox County emergency manager Laura Hintz told the Norfolk Daily News that Nebraska Highway 12, which connects Lazy River Acres with Niobrara and Verdel, could be flooded over soon.

In Montana, flooding near Hardin on Sunday morning brought down telephone equipment that handles 911 and long-distance calls for Glendive, Miles City, Sidney, Fairview, Colstrip, Forsyth, Wibaux and Terry.

Emergency calls were rerouted until full service was restored at about 11 a.m. Monday, Qwest spokeswoman Michelle Jackson said.

In the central Montana town of Roundup, houses and businesses remained under several feet of water from the Musselshell River, which first topped its banks and swept through town Thursday.

A mandatory boil-water order was issued, said Major Lori Hampa-Chamberlin with the Montana National Guard. Crews were working to pull stranded vehicles out of flooded areas and most routes into or out of the town were cut off.

"They're in trouble here," Hampa-Chamberlin said. "It's been raining nonstop."

The Musselshell River level had fallen about 6 inches by Monday. However, that drop was expected to slow with Monday's rain, said Brian Tesar with the National Weather Service in Billings.

Tesar said the expected warm-up later in the week raised the chances of flooding along the Yellowstone, Tongue, and Shields rivers in central and eastern Montana.