This winter season has been fluctuating in temperatures across the United States. With period of warmer spring-like temperatures and more seasonable winter temperatures occurring it can lead to winter flooding scenarios and ice jams on the rivers. Winter flooding can happen anywhere in the United States. Ice jams, coastal flooding and rapid snowmelt all can lead to winter flooding.
An ice jam is defined as pieces of floating ice on a river that are carried by the current which accumulate to obstruct the flow of the river. Ice jams form commonly just around the river bend and the mouths of tributaries. A tributary is a river or stream that flows into a larger basin of water like a lake or ocean. Ice jams form downstream of dams and upstream of bridges or obstructions because that is where there is a decrease in the river’s slope. The season for ice jams are usually late winter until early spring due to the fluctuation in temperatures. The constant melting and refreezing of liquid surfaces.
Ice jams can be defined in two ways. Freeze up jams which occur in early winter and break up jams that occur in early spring. Freeze up jams don’t usually cause much flooding but the breakup jams in early spring tend to cause the most damage and flooding. These break up jams lead to significant property damage like ripping houses off foundations and wooden decks.
Snowmelt contributes towards winter flooding because it adds water to the ground that drains in the same way that regular rainfall does. According to the National Weather Service in Des Moines, IA, on average one inch of fresh snowfall holds approximately a tenth of an inch of water so ten inches of snow could lead to five inches of water in the springtime. Other factors of snowmelt and winter flooding include high soil moisture from autumn, elevated stream levels, moderate-heavy rainfall while snow melting is occurring, and ice jams.
With this winter changing so rapidly it's important to keep an eye on any rivers or streams that may be rising suddenly. Paying attention to local weather reports and guidance from your local National Weather Service will help you be prepared for any ice jams or winter flooding!
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Photo Credit: NWS Riverton
© 2020 Meteorologist Shannon Scully