Friday, December 23, 2016

Huge Snowflakes Friday Evening

It looked just like a snow globe Friday when the snow was falling.  The snow was quick to accumulate on the roads, but was beautiful to look at as it.  And the size of the snowflakes made it look even more magnificent.  But have you ever wondered why snowflakes are the way they are?  And what was happening in the atmosphere Friday evening to allow such huge snowflakes to fall?

When trying to understand what occurs in the atmosphere, we have to think three dimensionally.  An individual snow crystal is small in size and has six sides.  A snowflake is made up of several of these six sided snow crystals.  The snow to liquid ratio will determine whether a snow is more dry or more wet when it falls.  When the atmosphere is very cold and doesn't have a lot of moisture, the snow is called a 'dry snow'.  A dry snow has very little liquid within the snowflakes themselves (because colder air can't hold as much moisture as warm air) and tend to be smaller in size.  Because there isn't much liquid within the snowflake, it will easily break apart.  And that's why dry snow isn't good at making snowballs.

The opposite happens when a part of the atmosphere is very close to or just above freezing.  As the snowflake falls from the cloud level it will partially melt.  This produces a liquid film on the snowflake.  Kind of like 'glue' for other snowflakes to stick to it.  As the snowflake falls through the atmosphere, it will continue to collect additional snowflakes adding on to its size.  This type of snow can easily be packed together and is good for making snowballs.

Strong winds break apart snowflakes as they fall.  But when the wind is light snowflakes can continue to grow in size, especially heavy wet snow.  In fact, these types of snowflakes can grow to silver dollar size in diameter or larger!  Light winds prevent the snowflakes from breaking into smaller pieces, protecting the liquid film around them.

The image to the left is the sounding of the atmosphere from the Quad Cities National Weather Service Friday evening.  It's like a snapshot of the atmosphere, from the surface to jet stream level.  Temperatures are located on the bottom.  Locate the 0°C temperature line and follow it up through the atmosphere.  Notice how the green and red lines are pretty close to it, especially up to about 4500ft.  With temperatures so close to freezing, it allowed for these types of snowflakes to form.  Pretty cool!!

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