The National Weather Service had flood warnings and advisories in place the first week of January for parts of Madison, Beaverhead and Gallatin counties — and all of them resulted from ice jams.
The weather phenomenon — which is exactly what it sounds like — is common this time of year across Montana and the rest of the northern region of the U.S. And so is the subsequent flooding.
The ice jams and flooding near Ennis, Three Forks and Logan earlier this month occurred when temperatures fluctuated, explains Katherine Chase, surface water specialist with the U.S. Geological Survey.
"They can also occur during break up when the weather starts to warm and the ice starts to melt and the ice starts to move and jam at that time too," Chase said.
She says ice jams can happen when the river or stream first freezes up and the ice blocks water flow downstream, flooding areas upstream.
The jams can cause flash floods when they suddenly break up releasing a cascade of water and ice downstream. NBC Montana reported Monday that the lingering effects of the recent ice jam in Ennis has closed Lions Park for the foreseeable future.
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