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Sub-Zero Temperatures Followed by Warm Up Increase Potential for Ice Jams and Flooding

Fluctuating temperatures across Montana have already resulted in ice jam flooding in some areas of the state and is raising concerns for potential flooding along other rivers and streams.

"We urge residents to be observant to rapidly changing conditions and prepare for the possibility of flooding," said Traci Sears, the Montana National Flood Insurance Program Coordinator at the Department of Natural Resources and Conservation.

A period of sub-zero temperatures followed by a rapid warm up has caused ice jams. Ice jams – or dams – occur when chunks of ice clump together to block the flow of water on a river or stream. Ice jams and subsequent flooding are common this time of year through March when temperatures regularly fluctuate.

Additionally, ice jams occur during breakup when the weather starts to warm in the spring. As ice starts to melt and move, it can get trapped at bridges, bends, or narrower reaches of the river. Ice jams can also cause flash floods when a sudden breakup releases a cascade of water and ice downstream.

"The result can be dangerous conditions for those living adjacent to ice jams when the water has nowhere to go causing rapid flood with little or no warning," said Sears.

In addition to homes and private property, fishing access sites, roads, and hiking trails can be closed or threatened by rising waters.

Sears advises that it is important for residents living near a river or stream to have a flood evacuation plan and consider the following:

• Purchase flood insurance. In most cases flood insurance must be purchased 30 days be-fore a flooding event.

• Keep extra drinking water on hand. Flooding can compromise local water systems.

• Shovel or plow snow away from homes and structures.

• Be ready to transport valuables or, where practical, elevate them.

• Never walk out onto a frozen river or ice jam. Thermal currents in rivers are unpredictable and ice can become unstable in an instant, leading to injury or drowning.

• Keep a vigilant eye on children and pets to ensure their safety if you are recreating near rivers and streams in the winter.

To learn more about the National Flood Insurance Program, visit Additional flood insurance information is available from the Montana Commissioner of Securities and Insurance Office Flood Insurance at

The Montana All-Hazards Weather Monitor web site offers up-to-date information on stream flows and potential flood conditions:

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