Name: Holly H.
Date: September 2001
Why does snow appear to melt at different rates given the
same height and temperature with similar amounts of sunlight?
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 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.
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Update: June 2012