What makes those snowflakes so large?
It was a bit of a surreal scene around Seattle as the snow fell Monday afternoon as some reports came in of extremely large snowflakes, such as those featured by Mike Mclaughlin of Burien:
And closer to the heart of Seattle:
The massive snowflake clusters are caused when temperatures are right near freezing. As the snow falls from the sky, but then encounters 33 or 34 degree weather, the snowflakes begin their melting process. As they do so, they become coated with a thin layer of water which in this case acts a bit like glue. In the chaos of falling snowflakes, instead of them just harmlessly bouncing off each other, they begin to stick to each other.
If the wind is nearly calm, as it was here, it won't blow apart the clusters, leaving you with "snowflakes" that appeared to be as large as 1-2 inches in rough diameter.
So when you see the big flakes, it's a sign that your snow is just on the fringe of being rain instead. In this particular case, the big flakes indicated we we were warming up, but snow shower passed before it could finish the change into rain.