Ask the Meteorologist: Snowflakes

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What causes snow to be light or heavy and what causes snowflake size and shape?

Keith Hull

Rogue River High School

There are two types of snow, wet snow and dry snow. Wet snow tends to be heavy and normally will bring larger snowflakes to the surface. Dry snow on the other hand falls in very small snowflakes.

To determine whether or not we will receive wet or dry snow, we must look at the temperatures of the atmosphere as a whole. Typically dry snow falls in the heart of winter, when the entire atmosphere is very cold. Wet snow though, falls in the beginning and end of winter …most of the time. This is because the atmosphere is still cooling down from the fall & at the end of winter, starting to warm up for spring. This in a sense “warmer” atmosphere does not allow for the snowflakes to be as tiny ..and a more liquid (as opposed to solid (ice crystals) like dry snow) wet snowflake will fall to the surface.

Also, although dry snowflakes are smaller than wet snowflakes …they tend to produce more snow accumulation. This has to do with snow ratios and is often looked at during winter storms by meteorologists. Dry snow has a high snow ratio — 20:1. This means that for every 1″ of liquid water falling from a cloud (imagine the snowflakes had been melted) about 20″ of snow will accumulate. With wet snow, the ratio is much smaller …about 5:1. So, for every 1″ of liquid water falling from a cloud, only 5″ of snow will accumulate.

Meteorologist Alyssa Caroprese