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Name: Holly H.
Status: Educator
Age: 20s
Location: N/A
Country: N/A
Date: September 2001


Question:
Why does snow appear to melt at different rates given the same height and temperature with similar amounts of sunlight?



Replies:
Holly,

There are many factors that affect snowmelt rate.

The angle of the Sun to the surface is a good example. Notice the amount of snow on the sloped sides of an east-west interstate highway. The south side will have more snow left because it does not receive as much sunshine and receives it at a lower Sun angle than the north side. The greater the angle of the Sun to the surface, the less energy it receives from the Sun.

The type of snow also has an affect. If the snow is light and fluffy ("dry snow") it may not melt as fast as heavy, "wet" snow that has more liquid water in it. A light, fluffy snow also allows more light to filter through it, thereby distributing the energy through a greater depth of snow, whereas wet snow absorbs much of the Sun's energy near the top of the snow and therefore it melts at the top; the melted snow drips through the snowpack, making it "wetter" and icy if temperatures drop well below freezing.

The dirtiness of the snow makes a big difference. A new snow reflects more light than an old dirty snow; the old snow will absorb more of the Sun's energy and therefore melt faster.

David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory


The melting of snow is a very complex process. Some (but not all of the factors, for sure) are: flow pattern(s) of the water from melted snow which tend to be random and chaotic, wind that can push snow and / or water in a preferred direction, the topography of underlying terrain that can make the apparent snow depth different than the topography of the snow itself, the deposition of water soluble solutes that can change the melting point of the ice from one spot to another, differences in the packing density that result from wind and / or rate of deposition of the snow, and so on.... and on.

The short answer is the process is pretty complex.

Vince Calder



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