Weatherz School: Snowflakes & snow ratios
You’ve heard it before, “no two snowflakes are alike.” Of course, scientists can’t possibly put every flake that flies under the microscope, so how can we be sure?
The type of snowflake depends on the temperature. Snow crystals can take a number of forms such as plates, needles, columns, and dendrites.
Because snow crystals are so sensitive to atmospheric changes, and because all snowflakes fall along slightly different paths, to have two snowflakes with the same history of development is virtually impossible. Two snowflakes can be very similar, but not identical.
Going back to snowflake types, dendrites are formed between about 3°F and 10 °F. This temperature range is the most efficient for ice crystal growth because it’s cold enough for a process called deposition: This is a phase change directly from gas to solid. We go from water vapor to ice crystal without a water drop.
Temperatures also play a key role in determining how much snow we get. The snow ratio is the amount of snow that falls for one inch of water. With temperatures near freezing, one inch of liquid precipitation is five inches of wet, heavy snow. An average snow ratio is about 10 to 1. But with cold air and dry snow, you can get a whopping 20 inches for the same amount of moisture. In extreme cases, we can get a lot more that.
On January 14 to 15 in 2022, a band of lake effect snow set up over Duluth with an incredible snow to liquid ratio.
1.4” of snow fell with a liquid equivalent of .01”. This is a snow to liquid ratio of 140 to 1. At that rate, a full inch of water would produce 140 inches of snow.
Snow ratios are part of why forecasting for snow can be so challenging. Just like snowflakes, every snow forecast is unique.