John Wheeler: Snow flurries happen easily but are hard to forecast
All that is required is a subtle rising motion in the air or a subtle cooling of the air at cloud level.
FARGO — 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.
With so much supercooled water available, it is very easy for snowflakes to grow, particularly if the weather is cold. 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 two or even more, even without the presence of any true weather system in the area.