Winter is around the corner. Time to get prepared.
The following web story is a direct transcription from the National Weather Service regarding winter weather awareness week. We are an important partner with the National Weather Service to educate and remind everyone about the many hazards that a New York winter brings and how to keep safe for the winter season. This is the fourth of a five part series on winter weather safety. Today’s topic will focus on one of the most deadly winter weather events central New York can experience: Flooding.
In upstate New York one usually associates snow, ice, and biting cold with winter. But sometimes nature throws a curve at us with unseasonable warmth and 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. Often, the warmer air will rise over colder air trapped in the region. As this air rises it results in clouds and rain, which will combine with the melting snow to increase flows in the rivers. When this melting snow combines with heavy rains it can put enough water into the rivers to send them over their banks.
Some of our worst winter floods are caused by intense cyclones that track from the Ohio valley northeast up to the Saint Lawrence valley into Canada. These storms bring a lot of warm and moist air into the region off the Atlantic, bringing both mild temperatures and heavy rain to the region.
In April 2005, the Catskills saw some of the worst flooding on record. The combination of five to seven inches of rainfall on top of a snowpack containing two to three inches of additional water produced record river flows at some locations. Sullivan County crested at 17.97 feet on April 3rd, 2005 which, up to that time, was the highest level recorded at the gauge since 1975.
Another winter problem in this area is flooding caused by ice jams on the rivers. As river flows increase, water levels rise. Since ice that covers the rivers is lighter than water it will tend to float. Under the pressure, it will often break into huge slabs. These slabs will then move downstream in the river current until they run into an obstruction such as a bend, island, or wide shallow area. When this happens the ice will often stop and pile up into a jam. When the flow of the river is blocked by an ice jam, the water can overflow the river banks in less than an hour as it tries to get around the ice.
As the water rises, the pressure can break the jam and release a sudden surge of water and ice down the river. While ice jams often form in the same spots year after year it is nearly impossible to predict exactly when or where a jam will form, or when one will break. Sometimes a jam that forms in early winter will stay put most of the winter. Severe flooding of roads and built up areas can also occur when mounds of plowed snow and ice block and plug up the grates and storm drains, so the water from the pavement has no where to go. This standing water can cause dangerous black ice if it freezes.
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