What Is Artificial Snow

Depending on how you look at it, artificial snow is either a blessing or a necessary evil.  Even in Utah, it has become essential to start the ski season in most years and ensure coverage in heavy traffic areas during the season.  Natural snow is far superior for skiing, but even I've learned to live with the reality that we are lucky to have snow from hoses.

Snowmaking at Deer Valley

Utah likes to say that it has the Greatest Snow on Earth, but it also has some of the Greatest Snowmaking Weather on Earth.  For snowmaking, it's not the temperature that matters, but the wet-bulb temperature.  The wet-bulb temperature is the minimum temperature that air can be cooled through evaporation.  It depends strongly on the humidity.  When the humidity is low, the wet-bulb temperature can be several degrees or more lower than the actual temperature, sometimes enabling snowmaking when the temperature is actually above "freezing." On the other hand, when the humidity is high, snowmaking can be difficult when temperatures are just below freezing.  

Thus, Utah's arid climate means we often have low humidity, and that helps with the snowmaking.  When I took the photo above, Deer Valley was pumping out the artificial snow like there was no tomorrow and the wet-bulb temperature was about 15˚F.  

I often say that artificial snow isn't really snow at all.  It is comprised ice crystals, but one difference from natural snow is that the ice crystals don't experience growth through what is known as deposition.  Deposition is the direct conversion of water vapor into ice.  It is the process through which those beautiful six-armed snowflakes and many other ice crystals form. 

Real snow can also grow through a process known as accretion, which is the gradual accumulation of mass as supercooled cloud droplets freeze on contact with larger ice crystals.  At the extreme, this leads to graupel.  

Cloud droplets are, however, extremely small.  A typical cloud droplet is 20 microns in diameter.  This is smaller than the diameter of a human hair, which is about 70 microns.  Thus, cloud droplets are incredibly small and it takes enormous quantities of them to produce a graupel particle.

In contrast, artificial snow is comprised of frozen water droplets.  These droplets are relatively large with diameters of 0.5 and 2 mm.  That's 25 to 100 times bigger than a cloud droplet.  Sometimes they stick together forming an aggregate of frozen droplets.  Below is an example of the aggregates of artificial snow droplets that fell on my sleeve when I skied beneath the snowgun in the photo above (click to enlarge).  Note that there are no plates or tree-like arms.  Just lots of frozen droplets.  

As a result, artificial snow is very dense, typically with a water content of 22–28%.  For comparison, freshly fallen snow at Alta is 8.4% and at the Central Sierra Snow Lab at Donner Pass in the Sierra Nevada it is about 12%.  So artificial snow is much denser than most forms of freshly fallen natural snow.  This is true even if the artificial snow is relatively "dry" with very little liquid water.  You couldn't make a snowball with the artificial snow above because it was too dry, but I could also barely push my pole into it because the density was so high.  

That density is a blessing and a curse.  It enables artificial snow to be extremely durable.  It isn't skied off easily.  However, it also makes for a much harder skiing surface that can polish up into a skating rink.  

One thing is for sure.  Love it or hate it, artificial snow is here to stay.  If it's critical for skiing in the current climate, its importance will only grow in the coming decades.  However, a group led by Peter Veals, a research professor at the University of Utah, is working to produce artificial powder.  Check it out here: https://www.quantum-snow.com/.