The Yellowstone River in Billings is expected to crest nearly 18 inches above its all-time record flood stage next week, according to updated forecasts released Thursday.
The forecast represents a substantially more dire scenario than the flooding expectations on the river that had been forecast just one day earlier, and has sent Yellowstone County officials scrambling to prepare for the river to hit major flood stage in Billings for the first time since record-keeping began.
Forecasts now anticipate the Yellowstone will reach its minor flood stage of 13.5 feet by Monday, and then rise to 16.4 feet late Tuesday or early Wednesday. "Major flood stage" at the river's gauge in Billings is classified as the point at which it reaches 15.5 feet.
The all-time record of 15 feet was set in June 1997.
"If we've got a foot and a half above that, there's going to be a lot of people in a lot of places that have literally never seen (flood) water before," said Yellowstone County Disaster and Emergency Services Coordinator Brad Shoemaker, speaking to county and city officials during a meeting at the county courthouse Thursday afternoon.
Heavy rainfall coupled with warm weather accelerating high-elevation snowmelt in south-central Montana had already prompted minor flooding this week in several rivers and streams that flow into the Yellowstone.
But Keith Meier, the meteorologist in charge at the National Weather Service's Billings office, said during a Thursday weather briefing that more than 2 inches of additional rain is possible along the Beartooth Front, and will drive the majority of flooding on area rivers.
"This setup has our attention, mainly for the hydrologic response on already high-running rivers," Meier said.
The majority of rain is expected to fall beginning Sunday and continuing through Monday morning.
In Billings, widespread flooding in residential areas is likely as stormwater begins backing up, Shoemaker said.
"That water could appear in a lot of areas, including more urbanized areas that don't seem like they're that close to the river," he said after the meeting.
And the flooding could also impact municipal water systems, according to public works director Dave Mumford.
"The problem will be at the wastewater plant once we get to 15 (feet), we'll be underwater, so we'll have to start pumping out of the plant," Mumford said. He also raised concern that the NorthWestern Energy substation near the plant could also be affected, given the current forecasts, and cause power outages in the city.
Butch Larcombe, a spokesman for the power company, noted that although such flooding would be unprecedented, NorthWestern doesn't expect outages. The substation serves about 1,800 customers in Billings, he said, but the utility would be able to re-route power to them in the event it goes offline.
"We're keeping an eye on it, but we're fairly optimistic that we're not going to have problems there," Larcombe said.
Mumford said when the river reaches just 14 to 14.5 feet in Billings, storm drains will begin to flow backwards, and manhole covers on city roads could begin getting pushed out.
"Stormwater is going to be the big one," he said. "We may have some manholes that will suck your car in, but hopefully if it's geyser-ing out, people won't try to drive in."
During the next few days, officials will be preparing maps to determine what parts of the county are most at-risk for flooding, Shoemaker said. His office has also requested about 50,000 sandbags that will be made available to county residents.
As river levels begin to creep up into flood stage Monday, he asked that residents call 911 if they see serious flooding issues and prepare their property for possible inundation.
"If you've got property in low-lying areas — cows, equipment, cars, anything you don't want to be in Miles City by the end of the week — now's the time to move it," Shoemaker said.
Rainfall is expected to cause flooding in small streams including Canyon Creek, Blue Creek, Alkali Creek and Pryor Creek. Irrigation ditches and other water transporting systems could be breached as a result of flooding, and their operators are asked by the county to monitor for signs of breaches and failures.
In a press release issued Thursday afternoon, Shoemaker said flooding could cause "bank erosion, channel migration, road and bridge closures, power outages and impacts to services such as water and sewer systems."
Yellowstone County plans to begin placing sand and sandbags for residents to fill at the following locations in the next couple of days: Huntley fire station, Worden fire station, Blue Creek fire station, and the Laurel soccer field at Fir and East Maryland Road.