Flood risk rising as warming trend looms

An icy Yellowstone River is seen Tuesday from the Highway 59 bridge near Miles City. Warmer temperatures over the next few days will increase the chance for ice jams that can cause flooding. Star Photo/Elaine Forman

Warming temperatures are coming and so is the potential for flooding and ice jams. The warming trend is expected to begin on Thursday.

Warning Coordination Meteorologist Tom Frieders of the National Weather Service’s (NWS) Billings office said the NWS watches for warmer temperatures for an extended time frame, like five days.

“That’s when the ice is going to break up and move,” he said.

Thursday’s high is expected to be 37 degrees, according to NWS, and The Weather Channel predicts that the highs for the following 12 days will be above freezing, reaching the low 40s.

Frieders said the ice jam season is usually mid-to-late February through March.

While last week there was no sign of a warming period coming, he said, this week is a different story. 

“It looks like our pattern is changing, with trends toward above normal temperatures into the middle part of February,” he said Tuesday morning.

The National Oceanic Atmospheric Administration’s 8-14 day temperature outlook map on Monday afternoon showed  this area is expected to see a 50-60 percent increase over the normal temperatures for Feb. 14-20. 

“In any event (whether this mid-February snowmelt is enough to break up the ice or we have to wait for a more significant warm-up into March), people need to prepare now for the possibility, since exact timing of when the ice will break up cannot be timed exactly,” Frieders wrote in an email. 

Frieders said the recipe for an ice jam is the combination of increased water flows and a thick ice cover.

Snow melting in the mountains creates increased water flows but so does local melting. Water from melting snow that flows down to the river and runs across the river ice will accelerate melting and possibly cause ice to jam.

Even if a river isn’t completely frozen over in one place, it could still have jams from ice coming from upstream.

According to a Montana Department of Natural Resource and Conservation (DNRC) news release “Montana experiences the highest number of reported ice jams in the continental U.S., with most occurring in February and March,” said DNRC Director John Tubbs. “Flooding can happen in any community and it can happen quickly. Residents in flood-prone areas should take steps to safeguard their families and properties.”

Frieders said eastern Montana is definitely seen as an at-risk area.

The confluence of rivers, bridges, and big bends in the rivers, are areas where big chunks of ice can jam up and Miles City has all three factors.

Though no one knows if there will be any ice jams here this season, Frieders stressed it is important to plan ahead and watch for warnings.

“Miles City has been more susceptible to ice jams in the area,” he said.

In March 2014 there were “quite a few ice jams” in eastern Montana and Miles City experienced flooding. 

That month the Yellowstone River rose 8 feet in 15 minutes in Glendive, causing damage to structures. 

In the 2015-16 winter there was “zero concern” for ice jams because the weather was real mild, Frieders said.

“This year is the exact opposite of last year,” he added.

While this winter started out mild, with November 2016 being one of the warmest on record, the prolonged cold spell since the middle of December thickened the ice cover on many of the rivers, slightly elevating the risk of flooding, he explained.

Frieders said it’s important to make residents aware of the danger now so they can plan ahead. 

Anyone in low-lying areas needs to move their livestock, equipment and other valuables to higher areas “because they won’t have time when it happens,” he said.

DNRC floodplain specialist Michelle Phillips said it is important for residents living near a river or stream to have a flood evacuation plan. She also advised keeping extra drinking water on hand, shoveling or plowing snow away from your home and structures, and being ready to transport valuables or, where practical, elevate them. 

The Montana All-Hazards Weather Monitor website offers information on stream flows and potential flood conditions at http://www.wrh.noaa.gov/byz/state/current.php?wfo=tfx.

If people prepare now, then there’s a chance that if any flooding occurs, it would have ”a minimal impact,” Frieders said.

“We’re prepared,” Miles City Public Works Director Scott Gray said Tuesday morning. “We have everything in place in case we get storm water.”

On the northeast edge of town, where storm water from Haynes Avenue flows to the Yellowstone River, two large 20-inch diameter inflatable “bladder bags” are installed to prevent any river water from flowing into the community if the river gets high, he said.

Storm water check valves, which also prevent river water from flowing in, have been inspected to ensure no debris is blocking them open. 

Local Disaster and Emergency Services Coordinator Bud Peterson is watching the state Department of Emergency Services situation report and while it’s a little early for news of flooding and ice jams with temperatures still well below freezing, he said, “I’m sure it’s looming on the horizon.”

In most cases, federal flood insurance must be purchased 30 days before an event for coverage to be in effect, the DNRC’s Phillips said.