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The original item was published from 11/24/2014 11:13:44 AM to 12/9/2014 12:05:01 AM.

News Flash

Butte-Silver Bow

Posted on: November 24, 2014

[ARCHIVED] Ice jam season underway- be prepared

Winter is here, along with ice jam season. Ice jams are formed as a result of long cold spells that cause portions of rivers and streams to freeze. Fluctuations in temperature or water level can break the ice into chunks which can jam at any obstruction as they move downstream.

These jams dam the water resulting in flooding upstream and can release very suddenly causing a surge of flooding downstream. Montanans should be especially concerned as Montana is the state with the highest number of reported ice jams in the Continental U.S., followed by New York and Wisconsin. This superlative is based on data from a US Army Corps of Engineers website.

In Montana, ice jam season starts in December, in the western part of the state, west of the Continental Divide (CD). In this region, there is a significant and nearly an equal number of ice jams that occur in December and in January. Still, the greatest number of recorded jams occurs in February and only a few occur in March.

Ice jam season east of the CD lags behind the season in the west. Only a small number occur in December. The risk grows into March, when nearly half of all the past reported ice jams occur.

Residents close to rivers and streams should have a plan. It is possible that they could become isolated or have to evacuate quickly due to flooding. Keeping a survival kit handy and ready to go is another aspect of being prepared for ice jam season.

In most cases, flood insurance needs to be purchased 30 days prior to a flooding event, such as an ice jam. Officials with the Montana Floodplain Management Program want residents to be aware of this flood risk. According to officials, flooded property owners express regret at not having purchased insurance or having purchased it too late. Many past flood victims were not aware that homeowners insurance does not cover damage from floods. There are currently 31 companies and countless agents in Montana that sell flood insurance through the National Flood Insurance Program. Residents that have a risk of getting flooded quickly from an ice jam are encouraged to talk with their insurance agent.

For more information about ice jams in Montana and the Montana Ice Jam Awareness Day in January, visit the National Weather Service website at

More on Montana Ice Jams from the NOAA
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