National Weather Service United States Department of Commerce

Fluffy snows are expected today and tonight, producing accumulations with very little water. Commonly, the percentage of water to snow is called the "snow ratio". An old rule of thumb was that for every 10 inches of snow, there would be 1 inch of water (10:1). However, this is far from the norm, and recent studies indicate that a 12:1 ratio might be more representative (on average) for the Upper Midwest. This said, there are so many variables that can affect the ratio of liquid water to snow that using a rule of thumb is usually off the mark. In fact, the snow ratios can change dramatically within a snow event itself. Some of the variables that come into play include...

  • Depth of the warm layer from the surface into the snow producing cloud. The warmer it is (closer to freezing), the lower the ratio will be.
  • Amount of ice in the snow producing cloud. If there is more super cooled water droplets in the cloud, snow ratios will be lower. If there is a higher amount of ice crystals, snow ratios will be higher.
  • If its windy, snowflakes can fracture, losing their "lacy" structure and leading to lower accumulations (lower snow ratios).
  • Deep cold, in general, promotes higher snow ratios.

With the very cold air in place across the region at this time, snow ratios today and tonight closer to 20 to 1 are expected, athough they could be higher.