Tuesday, January 18, 2011

Sleet & Freezing Rain- What's the Difference?

As posted on Syracuse.com by Drew Montreuil, 1/18/11

With icy conditions impacting Central New York this morning, meteorologists have been tossing around words such as "sleet" and "freezing rain", but what are the differences between these icy precipitation types?

For my Honor's Program thesis at SUNY Oswego, I have been investigating how the general public interprets weather forecasts, and what terminology is and is not understood. One of the survey questions I used to gather this data directly relates to today's weather.

When asked what is the difference between sleet and freezing rain, my preliminary results show that only 16% correctly understand the difference. If you do not know the difference, do not feel bad- only a little over half of the meteorology majors I surveyed fully understood the difference!

So, just what is the difference? When the water freezes. Sleet typically starts out as a snowflake while it is in the cloud. As it begins to fall, it melts into a rain drop. However, the melting is brief and, before striking the ground, it refreezes. Thus, sleet is simply falling ice pellets.

Freezing rain, on the other hand, does not fall as ice. Like sleet, freezing rain often starts off as a snowflake in the cloud, and then melts as it begins to fall. The difference here is that there is enough warm air in the atmosphere to prevent the rain drop from freezing on its way to the ground. When the rain drop does reach the ground, it freezes, typically within seconds of contact. There is one important condition for this to happen though: the air temperature at the ground must be below freezing.

While both sleet and freezing rain can cause slippery roads, it is the freezing rain that is typically more hazardous. Since sleet is already frozen when it falls, it can be plowed and shoveled with relative ease. The freezing rain forms a coating of ice on roads, cars and power lines, making it much more difficult to remove. A few inches of sleet is not a huge deal, but even just half an inch of freezing rain can bring down trees and power lines and create a very dangerous ice storm.

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