Hi, I'm new to this forum, at least in terms of posting although I like to follow Tony Crocker from time to time inc the best snow website as that man is definately in the know.
This is a post regarding what constitutes the dryness of snow.
Although I know the snow is consistently very dry in the Colorado area and significant part of interior North America in general, I was never satisfied with the marketed explanations as to why this was so. The four main explanations used are altitude, how far from the coast, i.e the higher the dryer, the further from the coast, the drier, the dryer the air the dryer the snow and the colder the air the dryer the snow. This just didn't sit well with me. For one thing I am from Europe and mainly ski in the Alps, the Alps have plenty of ski resorts that go just as high as Colorado's highest, the Alps are significantly colder than Colorado (on an altitude comparison), Colorado actually sits in the sub-tropics on the same latitude as Central Portugal, and yet from experience the snow is consistently dryer in Colorado. I would compare most of the ski areas I have skied in the Alps to have snow conditions more on average closer to somewhere like Whistler. So with this knowledge that the marketed explanations just didn't add up from my experience I was motivated to do a little research.
I looked into what makes snow dry? What I found was snow isn't really dry it’s perceived to be based on the water content of the snow and the water content is derived from the shape of the water crystals that form the snow. I found that light and fluffy snow is made up of branchy frozen water crystals whereas wetter heavier snow has less and even potentially no branching at all. So I asked, what factors influence how branchy the crystals are and to my surprise I found the greater the humidity the greater the branching and that the crystal believed to be responsible for super dry snow such as Champagne Powder is largely made up of Stellar Dendrite water crystals which are particularly branchy and refined and only form either very close to freezing (in the cloud - no good as will most likely melt before landing or shortly after) or at or very very close to -15celcius (in the cloud) in high humidity (in the air below); the higher the humidity the drier the snow. Then I Iearnt that the belief of; the colder it is the dryer the snow, isn't true either because humidity just cannot remain high much after -15C and then the humidity goes down, so does the potential for branching. What I also learnt is that the formation of snow is extremely complex (and that intricate details of snow formation are still being researched today. Bizarrely, snow crystals go from branchy to branchless (even if there is sufficient humidity) in temperature windows and scientists have no idea why this is. However it is well known that -15c and high humidity is the window for premium light dry powder snow. So the reason why dry snow hot spots score consistently dry snow is because they consistently hit the right balance of temperature and humidity.
So why is the interior of North America so good at hitting the 'sweet spot'. I think its partly to do with the fact that a lot of the mountain ranges, especially in interior USA are small and the mountains don't dramatically exceed each other. I put it to the forum that I am unaware of any consistent powder hotspots in ski areas that have particularly big snow verticals. So take the big glacier ski resorts in the Alps for example, the are not known for their consistent dry snow however some of the smaller ones on the edge of the chain, especially the North West where they are first in line for the majority of storms following the jet stream tend to get the driest snow. Flaine in France is well known, amongst us Europeans at least, for dry powder snow. I think the case in many parts of North America is the mountains (especially those from the smaller interior chains - especially in the USA) don't significantly loft the weather too high and therefore too cold (and dry). Take The Sierras in California for example, the majority of the weather following the jet stream has to go over some pretty big mountains, before it gets to the smaller Tahoe ski mountains, I believe the weather has been lofted too high. Same can be said for Mt Baker, small mountain, surrounded by huge glacier mountains that will loft the weather high but also suck more moisture out which partly explains the huge snowfall phenomenon. Take Alberta; the Banff ski areas or Jasper, they sit on the edge of the chain and are in direct firing line for a good radius of weather coming in following usual pathway of jet stream. However somewhere like Whistler has a huge amount of mountains (some of those mountains very big) that weather has to travel over before it reaches Whistler (based on usual pathway of jet stream), i.e coming down from Alaska rather than directly off the coast. In Russia Krasnaya Polyana, the resort for the 2014 winter olympics is said to get Japan dry snow and lots of it (plus in some seriously burly terrain) that is on the edge of the chain in peripheral mountains that are not dramatically big (no where near as big as the main spine). The Monashees / Selkirks look pritty good too in that there is a large region of flat land that weather will mostly have to travel over before hitting that chain. Utah's Wasatch, Bridger Bowl Montana, Taos New Mexico, all on the edge of chains and the mountain ranges of the interior US, small and don't dramatically exceed each other.
Personally I believe this is what constitutes dry snow, it all makes sense, and fits together nicely from my experience.
I would love to get Tony C in on this as he is for sure the one in the know.