Lala Approaching Hawaii; Flash Flooding Risks; Excessive Heat

Lala, may become a hurricane, is expected to impact Hawaii this weekend. Heavy rainfall, strong winds, dangerous surf and localized flooding are expected. Heavy rainfall and flash flooding concerns from the mid-Mississippi Valley, Ohio Valley into the central Appalachians continues, with the threat shifting toward the mid-Atlantic later this weekend. Record heat continues for areas of the South. Read More >

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.

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Lala Approaching Hawaii; Flash Flooding Risks; Excessive Heat

What Are Snow Ratios?