Weather Words: Snowmelt Flooding

As winter loosens its grip and temperatures begin to rise, the transition from winter to spring isn’t always pretty. The frozen landscapes of mountains and valleys begin to transform. Snowmelt flooding occurs when warming temperatures cause accumulated snow to rapidly melt, overwhelming rivers, streams, and drainage systems. While a slow, steady melt is manageable, a sudden warm spell or heavy rain can trigger dangerous flooding, especially when the ground is still frozen and unable to absorb excess water.

The risk of snowmelt flooding is highest in areas with deep winter snowpacks, such as the northern U.S. and mountainous regions. Rainfall on top of melting snow can worsen the situation, rapidly increasing runoff and pushing water levels even higher. Many times, ice on rivers get stuck or become jammed, which blocks the water from being able to flow downstream properly, which exacerbates the flooding. Ice and partially melted snow can also become lodged in drainage openings, preventing water from clearing urban areas.

We have seen significant snowmelt floods in years past. with some of the most devastating floods in the U.S. occurring due to rapid spring thaws. However, cities along major rivers like the Mississippi and Missouri have battled snowmelt flooding for centuries.

Today, meteorologists have become very efficient in forecasting potential snowmelt floods and are able to warn residents beforehand, which has greatly reduced loss of life from snowmelt floods. While snowmelt is a natural and necessary process for replenishing groundwater and ecosystems, its timing and intensity can have major consequences.

Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.