GRAND RAPIDS, Mich. (WOOD) — With warmer temperatures in Wednesday’s forecast, experts are watching for the possibility of ice jams on the Grand River, which can lead to flooding.
Andrew Dixon, a service hydrologist with the National Weather Service office in Grand Rapids, says it’s not possible to predict ice jams with complete confidence because there are a lot of factors.
“The best that we can hope for realistically is trying to identify and anticipate the conditions that could lead to the development of ice jams and then try to just get people as prepared as we can,” Dixon said.
But he said the “roller coaster” weather West Michigan is experiencing has led to ice jams in the past.
Temperatures could get up in the 50s on Wednesday, which means about half the snow on the ground could melt. That snowmelt will bring about half an inch to three-quarters of an inch of water to the rivers, Dixon said.
On top of that, he said West Michigan is expecting about half an inch of rain Wednesday night. That much added water can lead to ice jams for a frozen river as the water starts pushing up against the ice.
“We all know ice floats in water and so as the water starts coming up in the rivers, at some point it’s fighting against the ice that’s essentially one big piece right now,” he said. “There’s so much force pushing up from that water that it causes the ice to break or fracture into some large pieces. And then they start going down the river.”
Dixon described what can happen next as a game of Tetris: Pieces of ice try to find spots to fit but they eventually start stacking on top of one another.
“The big pieces get hung up on something, more ice is still coming down the river, it all starts mashing together and blocking the amount of water that is trying to go down the river,” he said.
That can lead to flooding, like Portland saw in February of 2019.
The main area of concern for the NWS is the Grand River, Dixon said, along with medium-sized rivers — like the Thornapple River, Rogue Rouge and Flat River — that flow into it. The Kalamazoo River doesn’t have as much ice, he said, while the Muskegon River isn’t expecting as much snowmelt and rain.
As the snow melts, NWS will be watching the medium-sized rivers first, as it will take some time for the water to makes its way to the Grand River. As we get into the weekend and into next week, the focus will shift to the Grand River.
“This is not going to be a really instantaneous it-either-happens-or-it-doesn’t. We’re going to have a prolonged window where we need to be watching,” Dixon said.
The NWS will also be watching to see how much snow melts and how much rain actually falls, which would impact the risk of having an ice jam.
As it assesses the level of threat, it could issue a flood warning or flood advisory if necessary. If it does, Storm Team 8 will alert the community.
Dixon says if you see something that looks like it could be an issue on the river, you should contact NWS or your local law enforcement.
He added now is a good time to prepare for possible spring flooding. He recommended moving items to higher ground if possible.