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John Wheeler, Published January 07 2013

Weather Talk: Conditions make it hard to forecast snow flurries

Snow flurries are hard to forecast. A forecast of partly cloudy or cloudy skies with no mention of snow can leave the public confounded when the sky fills with feathery flakes. Forecasters try to make mention of the possibility of snow flurries, but this is harder than you might think.

For most of the winter, low clouds in our sky are full of air containing supercooled water vapor. This means the tiny water droplets are in liquid form despite actually being below freezing. This happens because the process of snow crystal growth in clouds is a relatively slow one. So with all this supercooled water available, it is very easy for snowflakes to grow. All that is required is a subtle rising motion in the air or a subtle cooling of the air at cloud level.

Snow flurries usually produce just a dusting, but it is not unusual for big, hairy flakes to accumulate a fluffy inch or so easily, even without the presence of any true weather system in the area.


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