By Laura Zuckerman
March 10 (Reuters) - Floods that washed out rural roads in central Montana left hundreds of people stranded on Monday and forced the evacuation of 30 homes in one small town, as forecasts predicted more rain and snow that could worsen conditions in the region.
The flooding, which saw water begin streaming over rural roadways near the ranching community of Roundup during the weekend, came as warmer-than-usual temperatures rapidly melted deep snows amid recent storms that brought abundant rains, weather forecasters said.
Floods also threatened to inundate three towns in north-central Wyoming where vast ice formations blocked the flow of the Bighorn River and caused it to spill from its banks.
In Montana, a network of dirt roads linking rural Montana neighborhoods and ranches outside of Roundup were submerged in water or washed out by Monday, making them impassable, said Tara Gates, volunteer with the Musselshell County Disaster and Emergency Services.
Governor Steve Bullock declared a flood emergency, allowing him to mobilize Montana National Guard troops and direct other resources to affected communities, and local authorities scrambled to devise plans to deliver food and supplies to an estimated 400 people who were cut off by the flooding.
Some 30 houses in Roundup, a town of 2,000 residents about 50 miles (80 km) north of Billings, were evacuated and dozens of people were warned to prepare for evacuating at a moment's notice as rapid melting of mountain snows and ice jams force the swollen Musselshell River to overflow its banks, Gates said.
"It just kind of happened overnight. At first we had water slowly coming in and then everything that could break loose did," she said.
It is the second time in three years that Roundup has faced severe flooding. Hundreds of residents were displaced and dozens of homes in Roundup were destroyed in 2011 during historic flooding in the Missouri River basin.
Conditions could worsen in coming days as a pair of Pacific storm fronts are expected to bring more rain and snow to central Montana and elsewhere in the Northern Rockies, said Chauncy Schultz, meteorologist with the National Weather Service office in Billings.
Volunteers in Roundup used sandbags to combat rising waters, which eroded portions of earthen flood-control dikes on some reaches of the raging Musselshell, a tributary of the Missouri River.
Montana has 30 counties under a flood warning, watch or advisory, according to the governor's office.
The U.S. Army Corps of Engineers deployed teams of inspectors to assess levees that protect the north-central Wyoming communities of Worland, Manderson and Greybull from flooding by the Bighorn River, the Corps said in a statement on Monday.
Flooding caused by ice jams has sent water into several neighborhoods in Worland and pushed water and ice within 3 feet of overtopping a federal levee in Greybull, Corps officials said. (Reporting by Laura Zuckerman in Salmon, Idaho, Editing by Alex Dobuzinskis and Lisa Shumaker)