More rain began falling Sunday on soaked Montana communities after more than a week of floods in the region, along with a heavy mountain snowpack and burgeoning dams, prompted states downstream to also prepare for flooding.

A break in rainy weather at the start of the long holiday weekend allowed Montana residents to clear flood debris from homes and roads, but the respite was not expected to last long. The National Weather Service predicted up to 3 inches of rainfall from Sunday to Monday in the wake of a previous storm that brought as much as 8 inches to some areas of the state.

Officials warned ongoing flooding could ultimately be the worst in decades for the state, with an unusually heavy snowpack in the mountains, persistent spring rains, and waterlogged ground incapable of soaking up any more moisture.

As much as 18 inches of snow is predicted for the region's Beartooth Mountains this week, said Marc Singer of the National Weather Service in Billings, and temperatures at lower elevations could be above 70 degrees by Thursday.

"No part of the state is expected to not have some type of flooding," Monique Lay, spokeswoman for the state Emergency Coordination Center, said in anticipation of more rain and melting snow. "It's statewide, corner to corner."

About 1,500 North Dakota National Guard soldiers also have been summoned to help in the flood effort there as residents in Bismarck, N.D., and nearby Mandan brace for mass amounts of water to be released in the coming weeks at Garrison Dam.