National Flood Safety Awareness Week, Day 3: Ice Jams and Snowmelt

The National Weather Service (NWS) in Grand Forks North Dakota Has declared Monday, March 14th through Friday, March 18th 2016 as Flood Safety Awareness Week. Each day during the work week, will feature important information about a flood safety related topic.

Wednesday’s Message…

Ice Jams and Snowmelt: Ice jams are common during the winter and spring along rivers, streams and creeks in the higher latitudes of the continental U.S. as well as in Alaska. As ice moves downstream, it may get caught on any sort of obstruction to the water flow. When this occurs, water can be held back, causing upstream flooding. When the jam finally breaks, typically because the ice is melting, flash flooding can occur downstream. Six inch thick ice can destroy large trees and knock houses off their foundations. Once an ice jam gives way, a location may experience a flash flood as all the water and debris that was trapped, rushes downstream. This is why it is important to know when a nearby river is impacted by an ice jam and to avoid the area until the ice jam has been resolved.

Snowmelt and the breakup of river ice often occur at about the same time. Snowmelt flooding occurs when the primary source of water involved in a flood is from melting snow. The northern tier states and mountainous areas of the U.S. are particularly susceptible to snowmelt flooding. The snowpack can store the water for an extended amount of time until temperatures rise above freezing and the snow melts. This frozen storage delays the arrival of water to the soil for days, weeks, or even months. Flooding can occur when the snow melts and there is more water than the soil can absorb. The run­off from the snowmelt will head for nearby creeks, rivers, lakes and reservoirs, and may cause these bodies of water to overflow their banks, inundating areas that are normally dry. Check www.water.weather.gov daily to stay up to date on areas experiencing flooding and ensure you can avoid them.

Learn more about staying safe when faced with flooding at www.weather.gov/floodsafety.

Photo courtesy of the Cass County (ND) Emergency Manager.