The extended cold weather has caused a buildup of ice on many Eastern Montana rivers and streams, including the Yellowstone River, according to the Montana Department of Natural Resources and Conservation.
That’s especially concerning in a state the National Weather Service says has the highest number of reported ice jams and ice jam-related deaths in the lower 48 states.
Typically, said DNRC floodplain specialist Michelle McNamee, two-thirds of ice jams in the state occur in February and March.
“Because of the cold spell, there may be some places that have issues in April,” McNamee said in a telephone interview from Helena. “That wouldn’t be completely out of the question.”
Joe Lester, meteorologist with the Billings office of the National Weather Service, said the weather pattern looks to continue below-normal temperatures at least through the first third of March.
“We’re going to see some warmer days this weekend, in the low 30s,” he said. “That’s not enough to cause anything to start moving.”
Average highs for this time of year normally are in the 40s, Lester said, 20 degrees warmer than what we've seen. The longer the warm weather holds off, the greater potential for a rapid warm up that could lead to ice jams.
“This area, on the lee side of the Rockies, we’re prone to see rapid temperature fluctuations, cold spells and then rapid warm-ups,” he said. “Those fluctuations can definitely cause problems.”
Another issue to consider, he said, is the percent of water in the snow, especially east of Billings toward Forsyth and Ashland. Two feet of snow on the ground contains an estimated 4 inches of water.
“With the ground frozen, that means when the snow melts it doesn’t go into the ground, it runs off,” he said. “So now is definitely the time for people to think about that and prepare for that if they need to.”
Brad Shoemaker, director of Disaster and Emergency Services for Yellowstone County, has been staying on top of the weather. Once conditions become ripe for ice jams, his department will keep an eye on threats to infrastructure and get the word out to landowners who might be affected.
Another consideration this year, he said, is the amount of snowpack. The Upper Yellowstone Watershed and the Bighorn River Watershed have the highest snowpack in the Western United States, at 167 percent and 169 percent respectively.
“Whether or not we see flooding this year depends on how that comes off,” Shoemaker said. “If we ease into the spring, that will be fine. With an early warm-up, there’s a potential we could see flooding.”
McNamee said one reason she gets people thinking about potential ice jams and flooding so early is for those in potential danger zones to consider buying flood insurance. In most cases, it must be purchased 30 days before an event occurs.
She also recommends people in the way of potential harm develop an evacuation plan, including what valuables they would take or, if they might not be able to leave, to be prepared.
“The thing with ice jams is they’re pretty unpredictable when and where they happen. Also they can occur very quickly," she said. "If (people) can’t get out it’s important to have water, food and flashlights in case it takes time for emergency officials to get there.”
McNamee also has tips for people who don’t live in the ice-jam or flood-prone area. Stay clear of the flooding area, report ice jams to local authorities and never walk out onto unstable river ice or drive through floodwaters.
“We always urge people to keep their distance,” she said.