One of our deadliest winter weather hazards is flooding, our focus in our Winter Weather Awareness Week stories with the National Weather Service office in Binghamton.
In the state of New York one usually associates snow, ice, and bitter cold with winter. But sometimes nature throws a curve at us with unseasonable warm temperatures, and with it, rain.
A number of different factors work together to produce floods in winter.
When unseasonable warmth comes to the region it will often melt much, if not all of the snow on the ground in the lower elevations. The melting snow will saturate the ground and also begin to swell the rivers. If the combination of unseasonable warm temperatures, heavy rain, and snow melt occurs, rivers may then rise above their banks producing floods.
Some of our worst winter floods are created by an intense cyclone that tracks from the Ohio valley, towards northeast, up the Saint Lawrence Valley into Canada. These storms bring a lot of warm and moist air into the region from the Gulf of Mexico and the Atlantic.
Flooding during the winter months can also be generated by ice jams. When river flows increase, water levels rise. Ice is less dense than water, thus ice floats. When enough pressure is applied by the river below, the ice will break. Ice typically breaks into slabs and floats downstream. When the ice interacts with an obstruction such as a bend, island, or a wide shallow area, the ice will often pile up into an ice jam. The ice jam then prevents water from freely flowing, and forces the water to rise, creating a flood. Ice jams can form any time during the winter season.
Flooding on roads and poor drainage areas can also occur when mounds of plowed snow and ice block grates and storm drains. Standing water can cause dangerous black ice if it freezes.
Winter Weather Awareness Week stories end Friday.