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Weather Talk: Wet snow is hard to forecast

Weather systems that produce a mixture of rain and snow can be devilish to forecast.

If the precipitation is heavy enough, a couple degrees of temperature can make a huge difference in the amount of snow that accumulates. There is a lot more to this than predicting the surface air temperature.

Precipitation in these cold weather systems almost always forms as snow in clouds well below freezing, so it is very important to be able to forecast the temperature of the air all the way down to the ground.

Further complicating this is a process known as evaporative cooling. Some of the precipitation will evaporate as it falls and this process cools the air, so heavier precipitation is more likely to fall as snow and precipitation falling through dry air is more likely to fall as snow.

Warm ground temperatures further complicate all of this because melting snow draws heat out of the ground, causing it to cool. This means a heavier snow is more likely to accumulate than a lighter snow.

John Wheeler

John was born in Baton Rouge, LA, and grew up near Birmingham, Alabama. As a teenager, his family moved to Madison, Wisconsin, and later to a small town in northeast Iowa. John traces his early interest in weather to the difference in climate between Alabama and Wisconsin. He is a graduate of Iowa State University with a degree in meteorology. Like any meteorologist, John is intrigued by extremes of weather, especially arctic air outbreaks and winter storms.  John has been known to say he prefers his summers to be hot but in winter, he prefers the cold.  When away from work, John enjoys long-distance running and reading.  John has been a meteorologist at WDAY since May of 1985.

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