Thursday January 9th, Montana’s National Weather Service offices are recognizing the eighth annual Montana Ice Jam Awareness Day (MIJAD). Montana Ice Jam Awareness Day's purpose is to help educate the state’s residents about potential problems that can result from ice jams and associated ice jam flooding.
See this video of the Gallatin River Ice Jam in Montana on December 7, 2013 courtesy of KBZK.com
According to MIJAD's webpage, Montana has the highest number of reported ice jams and the highest number of ice jam related deaths in the lower 48 states. Ice jams that occur in Montana comprise approximately 9% of the total for the continental United States! Nearly two-thirds of Montana’s ice jams occur in February and March, but can be a problem as early as December.
There are different types of ice jams that can occur. Freeze-up ice jams occur when prolonged sub-freezing weather allows an ice cover to develop on a river or stream. Break-up jams occur when the freezing weather is followed by significant warming, allowing the ice on rivers to break free and flow downstream. Jams typically form as ice accumulates at obstacles such as bends in rivers or bridge supports. Water can quickly back up behind the jam and cause flooding. Jams can also release very quickly, often causing flash flooding as the water stored behind the jam then rushes downstream. Snowmelt or rain on snow and the breakup of river ice often occur in tandem and can result in more intense flooding.
While many ice jams develop and release before causing significant flooding, some can produce prolonged, extensive flooding and cause considerable damage. If you see an ice jam, contact your local National Weather Service office, your county Disaster and Emergency Services coordinator, or your local law enforcement.
References and helpful links:
NOAA’s National Weather Service: http://www.weather.gov
NOAA’s National Weather Service in Great Falls: http://www.weather.gov/greatfalls
Ice Jam Page: http://www.wrh.noaa.gov/tfx/icejam/?wfo=tfx