Snowmelt Floods

January 15, 2001


Provided by: NOAA
Summary authors & editors: Jim Foster

Heavy snowfalls in late December and early January across the Middle Atlantic states of Pennsylvania, New Jersey and New York have set the stage for the possibility of snowmelt flooding for the first time in 3 years. The past fews days have brought above normal temperatures to much of the Middle Atlantic states. If this "January Thaw" continues, and the remaining snow melts over the course of a day or two, flooding can be expected. A snowpack 10 inches deep can hold 4 inches or more of water. Add this much water to frozen streams, and you have a recipe for flooding. Because the partially frozen ground cannot absorb much of the snowmelt, most of it runs off directly into ice covered streams and rivers. The above photo, taken by Pat Murphy of the National Weather Service, shows parts of Pittsburgh underwater in January 1996 as a result of the Allegheny River overflowing its banks. The 1996 snowmelt floods were perhaps the worst of the 20th century in the Middle Atlantic states.

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