Heavy Snow: A Flood in the Making | WeatherBug
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Heavy Snow: A Flood in the Making

February 19, 2020
By WeatherBug Meteorologist, Andrew Rosenthal
Although heavy snowfall may bring a white glint to the ground and makes for great skiing conditions during the winter, dangers lurk in the snowpack come spring.

After all, snow is made up of frozen water. On average, six inches of old snowpack will melt down to one inch of water, although this number can range from 3 to 15 inches of snow per inch of water. At the end of winter, the snowpack can be several feet deep, meaning that a great deal of water will be melted.

As temperatures rise above freezing, the snow melts and the water flows toward the nearest river, stream, or body of water.  When this torrent of water reaches streams, rivers and drainage systems, it can quickly overwhelm them, causing water to rise out of the banks, flooding adjacent land and roads.

Spring floods can occur anywhere downstream of large snowpacks. Especially prone areas are low-lying ditches and streambeds, where water becomes trapped. As the pool of water grows, it can turn rivers into monstrous waves capable of flooding everything in its path.

Large, flat valleys can also receive extreme floods, when a rapid snowmelt overwhelms a river.  Such was the case in 1997, when the Red River of the North was overwhelmed by snowmelt, flooding the Grand Forks, N.D. area for several weeks.

While large-scale floods are rare, they can cause damage in the billions. Smaller-scale flood events, such as those that occur when a stream overflows its bank, are much more common. While they may not cause damage to an entire community, a small flood can still hurt you or your possessions.

In the early 20th century, valleys such as California`s San Joaquin Valley would flood every spring, with the floods causing severe damage to large cities like Fresno. Dams have been built in the foothills to control the rivers and manage its flow, stopping the yearly valley floods. Many dams throughout the Western U.S. were built to prevent annual springtime flooding.

River water following winter snow melt can also be big trouble for swimmers, too. Water from the recently melted snow is very cold and swimmers can easily suffer from hypothermia. This causes their body to slow as their temperature drops, making swimming difficult. Additionally, the water levels are usually higher than normal and the river is often swiftly moving. This can quickly sweep away and drown even excellent swimmers.

Next week, the third week of March, is National Flood Safety Awareness Week. Take the time to consider the streams and rivers near you and what you would do if snowmelt led to a rapid rise in the water level.

Remember, while that snowpack might be pretty to look at during the winter, it can produce dangerous and deadly flooding comes spring time.