Ask A Scientist Weather Archive

  
name         Michelle C.
status       educator
age          40s

Question -   I understand that wind affects the melting of snow because the runoff can be 
driven into existing snow making it denser, therefore more difficult to melt.  But wouldn't stronger 
winds also contribute to quicker melting in above freezing conditions due to the removal of the 
insulating blanket of cold air over the snow? Also how much does wind contribute to the evaporation 
of melting snow?

Our local weatherman tends to make statements like "There is a lot of wind today, so we will not be 
seeing much of the snow melting."

Why would wind chill have anything to do with the melting of snow?
Wind blows away the layer of heat around us, how does it work with snow?
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The process of melting snow is very complex. Temperature (both air and ground), relative humidity, 
wind speed (can work either way), snow density, presence of salt and other "de-icers". Wind chill 
plays a factor because it is a measure of how much warm air is swept away from the snow. The snow 
melting process is an engineering nightmare!

Vince Calder
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Michelle,

Gravity is probably more effective in allowing melt runoff to percolate down through the snow than 
wind is.

Strong winds contribute to increased melting (or sublimation) of the snow by rapidly removing water 
vapor from the snow surface,
allowing drier air to come along and thereby remove more water vapor. Sublimation is the change of 
state directly from  a solid (like ice) to the vapor phase (water vapor), skipping the liquid phase. 
Sublimation contributes to snow removal, but is not really melting. The greater the wind speed, the 
more water vapor can be removed, and therefore the faster the snow will be removed. This effect is 
probably more important than the "wind chill" effect, which implies that the greater the wind speed, 
the more energy is removed
from the snow surface.

Wind chill is only important when the surface being cooled is warmer than the surrounding air. If the 
air is warmer than the snow (which is at around freezing all of the time), it will contribute energy 
to the snow to help melt it, as well as serve to remove water vapor from the snow surface.  If the air 
is cooler than the snow, no wind chill effect occurs and the wind simply serves to remove water vapor 
from the surface.  The exception to the latter occurs for very strong winds, where the air moving over 
the snow "deposits" energy at the snow surface because of frictional effects, thus, in a minor way 
helping to melt the snow.

As for the weatherman's statements, when he says that there will be a lot of wind, perhaps this will 
be accompanied by heavy clouds; if so, the snow melt will be slower because the Sun is not shining 
on the snow.  If he is thinking that high winds will reduce the effect of the Sun on the snow (by 
keeping the snow surface cooler), he is partially correct (as long as the air is not much warmer 
than the snow); however, the enhanced removal of water vapor from the snow surface by the wind will 
be much more dominant.

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

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Dear Michelle-

Lots of factors affect snow melting, and wind velocity is but one.  The temperature of the 
ground, and even the composition of the ground can affect the rate at which snow melts.  
Melting can occur even when the air is below freezing, if the snow is heated by the sun. 
And the albedo of the surface of the snow affects the melting rate also. Snow can also 
evaporate, when air temperatures are below freezing.

In most cases stronger winds with above-freezing temperatures will hasten melting, due to 
the mixing of the water vapor just above the snow surface with drier air higher up.

Wendell Bechtold, Meteorologist
Forecaster, National Weather Service, St. Louis MO
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